Ok so i finally had a chance to run my RPO codes. There's quite a few questions i have that HOPEFULLY i can get help with!! First ill start with the codes that said ERROR CODE NOT FOUND:
B3W, E7Z, NOD and 1HV.
YT9 came up but showed ??? thats weird. any got info on those codes?

Also theres a few codes that i cant understand the description (maybe im an idiot or just really tired)
MXO: Merchandised, trans, auto provisions, o/d thats exactly how it shows. wtf is that?
PB4: Lock control, wheel
1sc: package option 03
6ZX spring, computer selected, front, left hand
7ZX spring, computer selected, front, right hand
8NL spring, computer selected, rear, right hand
9NL compputer selected rear right hand spring
what the hell are all those?
and one last thing...My car was originally equipted with a 5.0 TPI auto. it has the G80 code for the 2.73 positraction limited slip. the car now has a 5.7tpi that was obviously swaped. BUT the car is a one legger. WTF?! any ideas? maybe i just need to service it or something i dunno any help here? i know im askin a lot but HELP!!! :-D

 

350 is prob a slug...because of the rear gears...you need to bump them up to a 3.XX gear set.

all the computer seleces "springs" is GM typing all your options and model and all that crap into a computer and the computer telling them what springs to use on all 4 corners...

i may be wrong on this...taking a stab...MXO...auto provisions...the cars came standard with a manual transmission...so it was merchandised that the consumer paid for an automatic transmission.

here's a start...lemme see if i can find any of the others for ya...
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YT9...i got "Option Package, Fisher Furnished Parts...that leaves me curious...idk.

1Sc refers to the package of options that were offered for that set year...what year is the car???

 

ya she's definitely in need of at least 3.43s or something. the problem is it's suppose to be a posi but only the right rear spins. the rear is dirty so i couldn't see if there was an lsd tag or not . since t the motor was swapped u think maybe the rear was swapped too. i don't know why someone wolfed do that though. maybe the posi unit iis bad? the car is an 87 btw.

 

anything is possible without documentation. I could say it has just been serviced and sell the car and they come to take it to a place and they tell them that there isnt even one in there so, like i said...anything is possible...maybe the rear blew out and they swapped it with something they had laying around...maybe it's not even a 2.73...until you take it apart to look at it...it's up in the air...

personally, if i was to swap the motor to a 350 and i had the 2.73s i would already be swapping in a 3.23+ posi rear in...even before i swapped the 350 in, but i didn't own that are nor did i know them so who knows, if it's sluggish it's probably a 2.73, i don't about 87, i know 88s, so i'm going out on a stretch, but in 88 you could get posi in any model, base to top, so i don't understand why someone wouldn't get an LSD for thier car.

If the right rear is the only one to spin then it's open or LSD isn't working. Only way to tell if the LSD is in there is to open it up at this point to check.

 

As 84redta pointed out the best way to know what gear/traction device is in the rear is to pull the cover.Another good thing in pulling the cover is you can change the gear oil and if it does have a posi unit don't forget the additive.

Also the axle code build date/plant was stamped into the passenger tube on the pinion side.It may or may not still be readable.

On the codes here's what i found.
E7Z - Key,Speedometer(Delete)
NOD - Assembly Plant,Norwood Ohio

On code YT9 remember interior parts are generally Fisher supplied.It just specifies the source.84redta take on code MXO is a good point as our cars were standard manual so the code show it would be an automatic.Going down the line the correct pedals,steering column and electrical were installed.

 

it definitely originally came with the posi because it has the g80 code. like you guys said only way to find out is to take the cover off. the rear is dirty *** hell so i don't think i'd be able to see if it's got the tag or not. at this point i think i'm screwed either way. if it is a posi unit then it's probably broken which means i gotta rebuild or get another one. or it's just an open rear and i gotta get another one. wat would the chances be for it to work if i do a flush and fill and add the additive?

 

what do you lose?? $5-10 if you do the flush and it doesn't work??? But honestly you already said the 350 was a slug so you probably need gears...def if you got the 2.73s. It's up to you, like i said...not much to hurt at least until you can afford rear swap. If you don't already have disks...look for disk, posi, and a good set of gears, 3.73 would be great. OOORRR...not sure how good they are quality wise, but i was looking up LSD's for our axles on ebay, and there is a DIY rebuild kit, gives you the gears you want, and 3.73 was on the list, rebuild kit on all the seals and everything, and a new LSD to rebuild the entire differential. So if you got disks already it woudln't be a bad route...but for $600 i don't know if it's worth it. So i would suggest doing a little research, they had 12 bolt, 10 bolt, and 9 bolt setups listed so there is a wide choice there.

 

ya im gonna just do the flush anyway. cuz like you said 5-10 bucks isnt gonna hurt you know? either way i need to do it. how much could i get a stock posi disk rear? ive seen some drum set ups on craigslist for as little as 150 bucks.
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btw thanks everyone for helping me out!

 

my best suggestion to you is to go to www.car-part.com, not sure, but i believe that works across the U.S. It will provide you with all your local junk yards that have them, they have very accurate steps to go through and select disks instead of drums and such. Otherwise i would suggest you going to a pick and pull yard. Around me rear axles are from $50 to $150, no matter what car they are from, no matter whats in them, so theoretically you could get a nice 3.73 set up of disks with posi, for say $100, but you gotta pull it yourself. Then again that is excelent to learn how to, or how not to remove something from you car so you don't break whats in your car. And they aren't marked up like regular junkyards would be becuase of "value" in the car or the more demand and all that jazz...Other than that, your probably looking $150 to $300, all the way up from there depending on internal gears and miles on the car pulled from.