For the rear end in my caprice (87 305, with 2.56 limited slip) to make it a 3.42 with posi what do I need, and can it work with the rear end I have now?

You'll need a 3-Series posi carrier (AFAIK, there is no "thick ring gear" suitable for a 2.56 carrier), some layout dye, a dial indicator and mag base, a crush sleeve, if you want, new pinion and carrier bearings, possibly some shims, a new cover gasket, a pinion seal, a yoke holding tool, and an accurate torque wrnech. You can get most of the parts in an "install kit" avaialble from many ring/pinion gear suppliers.

What is my rear end made up, like carriers and bearing sizes. its a GU8 the 2.56 open rear end.

Im just looking for a taller gear like 3.42. Will these fit in mine if I just got the ring and pinion?

I just dont wanna eat my rear end away when my new engine is put in,lol

What is my rear end made up, like carriers and bearing sizes. its a GU8 the 2.56 open rear end.

Im just looking for a taller gear like 3.42. Will these fit in mine if I just got the ring and pinion?

I just dont wanna eat my rear end away when my new engine is put in,lol

Shouldn't the 2.56 be a GM8? You can't put the 3.42 pinion/ring gear set directly on it due to the size of the carrier. BTW, a 3.42 is shorter not taller.

You could go up to a 3.08 (GU4) with that carrier. There's nothing wrong with the 3.08 - you get better economy than with 3.42s and still have enough reduction to facilitate easy burnouts.

Shouldn't the 2.56 be a GM8? You can't put the 3.42 pinion/ring gear set directly on it due to the size of the carrier. BTW, a 3.42 is shorter not taller.

You could go up to a 3.08 (GU4) with that carrier. There's nothing wrong with the 3.08 - you get better economy than with 3.42s and still have enough reduction to facilitate easy burnouts.
Sorry my bad on the GU8 it its GM8 (just checked my RPO)

Do I just need a 3.08 ring and pinion? I assume My rear is a 10 bolt. is it a 8.2 or 8.5?

As you can see, I know nothing of rear ends >_<

Sorry my bad on the GU8 it its GM8 (just checked my RPO)

Do I just need a 3.08 ring and pinion? I assume My rear is a 10 bolt. is it a 8.2 or 8.5?

As you can see, I know nothing of rear ends >_<

It could be a 7.5" or an 8.5" - if there's the RPO code on the SPID label for it, G87 means 8.5" and G89 means 7.5". First, I rarely see either of these codes on the SPID label of a CHEVROLET B-body, and when I do, it's always G87 + every 80s Chevy B-body I've pulled the diff cover off of had the 8.5" gear. That's not to mean that all of them are, I may have just gotten lucky a whole lot of times, but I do think there's a trend there. Buick/Olds/Pontiac B-bodies almost always have G89 on the SPID label which makes them 7.5", at least the ones I've seen.

what is this 3 series carrier? if I get that I can run dif rations besides a 3.08?

Could I just buy a eaton posi unit for a GM 10 bolt and pick my gear ratio with it?

A "3-Series" carrier has the ring gear backset spacing designed to accomodate a smaller diameter pinion gear than a "2-Series" carrier. There are (or, were) three different ring gear carrier backsets in Saginaw axles. The common ones are 2- and 3-Series. There is the possibility of using an aftermarket ring/pinion set which is designed to bolt to a 2-Series carrier and provide the correct pinion spacing, but they are only commonly available to replace a 2.73 gear set. The pinion gear is so physically large in the 2.56 axle that the ring gear thickness required to correct the spacing for a "3-Series" pinion diameter would be impractical. As a result, you'll need to acquire a "3-Series" carrier and the gears of your choice.

With a "3-Series" carrier you should be able to install 3.08, 3.23, 3.42, 3.73, and MAYBE a 3.90 gear ratio from the right manufacturer, as well as 4.10, 4.56, and 4.88 ratios.