Had a 305 with one-piece main seal T5 now is a 1979 350 with 2-piece main seal 350 the question is is there a difference between and witch one to get?

 

they switched to the one piece rear seals in 86, so order a 153 tooth flywheel for an 85 Camaro with a 305 and you will be set. you can get them in either standard like GM used in millions of cars from 1955-1985 or lightweight like they used in the 85 IROC.

 

Has to be a 12.8" one, Those only came into existence in about 78 or so. Earlier V8 cars all used the 14" size.

As said, 83-85 Camaro will get you what you need. You will find there is a choice between 2. 1 is about 22 lbs and was used in LG4 cars, to allow the severely under-powered motor to disturb the car marginally from a stop through the inappropriate gears they usually had. The other is about 16 lbs and was used behind L69 cars with 3.73 gears.

AFAIK there were no TPI cars, aka IROCs, with 5-spd in the only year of those (85) that would have used that kind of flywheel. I don't think you'll get real far trying to look it up that way.

You'll probably like the lighter one better, esp if you have 3.42 or higher gears.

 

most common low performance passenger cars had the smaller 153 tooth flywheel going back to the dawn of the small block- and even the legendary 302 powered Z/28s from 67-69 used the small flywheel and 10.5" clutch because it was lighter. and rockauto has (or at least had when i ordered mine 6 years ago) a lightweight IROC specific 2pc rms flywheel listed for the 85 model year only. i think i paid $65 for it then.
and don't forget the pilot bushing and hope that your engine isn't one of those oddball 350s that were built in the 70s that didn't have the rear of the crank drilled for the pilot bushing and the starter pad not drilled with the third hole for the straight across starter bolt pattern used on the smaller flywheel... don't ask me how i learned about those two cost saving measures that GM used in the malaise era..

 

just looked it up on rockauto. they show the same lightweight flywheel as being a direct fit for any 85 and earlier Camaro with a 305 and even the 69 with the 302, and they range from $50 to around $200 depending how fancy of a brand name you want to get.

 

You may find it "listed" that way, but it didn't COME that way.

302s CAME WITH the 14" wheel and 11" clutch. Their block wasn't drilled for the 12.8" starter bolt pattern. No such thing as "features from the future".

The bolt pattern on the block for the 12.8" starter, obviously a necessity for the 12.8" flywheel, was introduced in the late 70s; 78 let's say, for the sake of argument. Might have been 77 but I'm not sure. Oldest car I've ever owned that had it was a 78 El Camino 305 that my wife bought in about 82 or 83. My 78 & 79 Z28 350s for example didn't, the 73 400 block in my garage didn't, and so on.

83-85 Camaro/Firebird V8 will get you the right part. If it's "listed" for anything else, and is the same part number, then all that is gravy; but irrelevant as far as CAME WITH.

Your 79 350 block may or may not have the 12.8" starter bolt pattern drilled into it. Some do, some don't. My 79 4-spd (bought it in about 81) didn't. I don't think my 78 auto (bought that one in about 85) did either but I don't remember about that part of that car because I don't recall ever having to mess with it before I sold it onward. Don't pay too much credence to the starters you can buy that say "fits either flywheel size"; they neglect to mention that they fit the smaller size wheel IF AND ONLY IF the block has the right bolt pattern. They can't work magic.

 

not trying to argue, but i looked up several Chevy small block powered cars from the 60s on several different parts store websites to see if i was wrong about the 153 tooth flywheel and starters.
Novas, Camaros, and Chevelles with 283, 302, and 327 engines all had the smaller ring gear and matching straight across bolt patter starter listed, which jibes with my memories of pulling who knows how many of those cars apart over the years.
the 70s was the oddball decade where they put the bigger flywheel on most applications for whatever reason.
other than the lightweight flywheel that was designed for the 80 F bodies, there is nothing inherently special or different about these particular parts for these cars.