Looking into 2 options

1- Overhaul the existing 3.73 non-posi stock 10 bolt like ronusmc's
= (10 Bolt upgrade photos)https://www.thirdgen.org/forums/tran...de-photos.html

Excerpt from ronusmc's post:

This is a break down. Some of these parts are necessary for the build and some can be changed to match your personal preference as in brand and style L.S.D./Locker.,etc.
3.73(I added that figure, Ron's is 3.42) ring and pinion =$ 200.00
master bearing kit = $ 90.00
axle bearings and seals = $ 30.00
28 spline Eaton posi. Unit = $ 500.00 ( highly recommended )
28 spline axles = $250.00
installation/labor = $ 300.00
and if you want ,a LPW Ultimate support cover = $ 160.00 ( also highly recommended )
Thats $1,530.00 counting the cover.

OR

Go with an austrailian 9-bolt with posi 3.23 gears off of a 87 GTA. PBR brakes. For about $300.
9 bolt appears and specs out to be in good shape.

I drive hard. I will beef up the 305 with headers, etc..then eventually get a 350.

What would be a good bang for the buck? At first I thought that the 9 bolt would be better but that means a 3.23 gear versus a 3.73. It also means that the currently "NEW" stillen pads/rotors and new calipers on my 10-bolt would bea worthless.
The goodridge brakelines on the 10-bolt may also be an issue.. waste of money??

So, when I think about building up the 10 bolt, it seems logical. But its still a 10-bolt.
Chuck

 

IMO, go 9" or equivalent. 9 bolts aren't much stronger than 10 bolts. If you plan on putting any bit of power to a 9/10 bolt rear for any length of time, you'll regret putting money into it. I got my Moser 9" for $2000 ready to bolt in, off the classifieds on here. I didn't just buy a bulletproof rear end, I bought peace of mind with it.

You could go with the 9 bolt, but that's just a bandaid and ticking time bomb, in my mind.

 

Ford 9" all the way provided you've got the funds. Investing money into a grenade is a waste of time. Rebuilding the stock rearend twice = complete 9".

 

i'm not sure why peaple keep saying the 9 bolt is weak. Take a look at our HDT/Brock cars of the late 80's early 90's and HSV cars all through the 90's, Ford were also using them in their performance packs. Maybe theres a problem with the diffs built in the US. As far as I'm aware all our axles and gears were shot peened and our 28 axles are monsters compared to the 25's. One of the first things we do though is shim the cones, the factory setting would wear the cones quickly. I've got three 9 bolts, 1 in my daily driver, 1 in the car i'm building and 1 in a car I'm stripping out, all three have left countless twin stripes behind them. You can also get a huge amont of ratios, shims, cones, axles and bearings are dirt cheap, and if you want something stronger Eaton does a posi and you can get off the shelf full floater kits, then you could go 31 spline and your set for 700-800hp

 

It's not that the 9 bolts are weak, it's that they're just not a whole lot stronger than a 10 bolt plus in north america, upgrading to better performance parts in them isn't as cheap as what can be done in Australia. The only north american cars they were available in were the 86 to 89 f-bodys and not all models got them. That makes parts availability and supply/demand very low in NA. At the time, it was the factory performance option but with so much better aftermarket choicesnow, it's not the best economical option.

In the end, a basic 9" package will give a better bang for the buck plus upgrade parts are dirt cheap compared to other diff options.