I've been running a 1985 S10 mechanical speedo .72 OD T5 in my 54 truck behind a 235 for the past year and a half. I used a 3.42 88 Camaro drum diff with a 28" tall tire and the truck cruises at 2000 rpms @ 70 mph. I've documented the modifications necessary for the install of both the transmission and the diff in my webshots "shoebox" album. I run a tank of gas through the truck most weeks so it's not a garage queen....it's on the road most every day. My mileage averages 18-20 although the new E10 we're forced to run, has required a bit of re-tuning and some modifications to the fuel delivery system.
If I had it to do again, I'd really opt for a 3.73 which would let me cruise at max vacuum at between 60-65mph. The .72/3.42 combo lets me drop down to 45 mph in 5th without a downshift and accelerate with the normal flow of traffic. The 3.76 1st gear winds very quickly and you can putz around town in 4th gear at 35 mph with no lugging. I'm running dual carter/webers with Fenton splits through glass packs with an electric pump at the tank (E10) and fuel pressure regulated to 3.5 psi.
The .72 T5 came out of a 2.8L shortbed S10 and the driveshaft will bolt up to the Camaro diff with only slight modifications.
I run 5 lug on 4-3/4" 15X7 rims with 4" BS and a 235/70/15 tire on front and the same lug pattern with 15X8 rear rim with 4" BS with a 255/70/15 tire. There is ample clearance from the tie rods in the front and from the box and fender in the rear. The Camaro rear sway bar will adapt to the AD by mounting it on top of the diff housing. The 39" eye to eye width will require only two holes in the frame for the control links.
To answer your question about the S10 rear diff...the 4wd will work but the axle ratios are limited. If you do decide to use the Camaro be sure to salvage the emergency brake cables. They are easily adapted to the AD emergency brake system. Be advised that most any diff you choose will require cutting away coil spring pads and setting new perches and pinion angle. However, being able to cruise with traffic and get decent performance and mileage make the effort to convert well worth it. Hope this helps you with your planning.
Dave
