Hi, sounds like fun!
If you really want to use that early Firebird rearend, check it out
thoroughly first! I don't know what your idea of "early" is, but if
it's from the 1960s, it may be an oddball. I would recommend a 70-81
Camaro/Firebird rearend, with the 8.5" ring gear. Width should be
close, it may be an inch or two shorter than the stock truck rear. Used
rearends often have bad axles, and bearings, and if you are gonna tow,
you need to make sure it's all in tip-top shape...so take it all apart
and make sure it's right. (if you don't have the expertise to overhaul
a rearend, then get a shop to do it--it's usually not too expensive if
you don't need many parts)
On the front brakes, you just need the 53-54 car hubs and drums...but
there's an oil slinger in there, between the inner bearing and the brake
backing plate, that is the wrong size, so remove it completely if you
can't find the correct one from a car to use. You need the car bearings
for this setup (at least the inner one).
As for the rearend ratio you need for your truck...if you are gonna tow
with the stock 235, then you'll want to keep the 3.90 gear ratio (stock)
or maybe go to a 3.73 or 3.55 car rearend. If you are gonna swap in a
V-8, then you can go with a 3.08 or 3.36. There is a trade off
here...the steeper the ratio, the better it will haul weight, but the
slower you'll be able to go on the highway (because of how fast the
engine will spin).
To mount the rearend, you'll want to keep it below the springs...the 6
inch drop from mounting it on top is way too much for what you plan to
do with the truck. Cut the original spring perches off the old rearend,
and weld them to the new rearend, making sure you have the same pinion
angle and side-to-side spacing.
oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959