Rear End - I agree the 8-3/4" is fine for you + MUCH cheaper + MUCH easier to change gears. I believe the rear ends got wider in '71 (vs. '70 & earlier) in B-bodies. The '71+ ones "might" be the same as the E-body, but definitely wider than a '70 & under.
To go cheap, & just bolt in an assembled rear from another car, the #1 thing is to make sure the distance between the spring perches is the same as what you already have. The #2 thing is to make sure the rear end isn't too wide for tires/wheels to fit.
If you have a little more cash and/or don't mind cutting & re-welding spring perches and re-setting pinion angle, you can get more tire clearance by installing a '70 & earlier rear end OR maybe even an A-body 8-3/4" (a little tough to find).
In all cases, I think your driveshaft length will be off too, so you "might" need a different driveshaft as well. And don't forget, there are two different u-joint sizes. Oh yeah, there's something about the "iso-link" rear suspension that I think has to be addressed too.
It can be done. A shop put an 8-3/4" rear in my '77 Cordoba that had the iso-link rear suspension.
Manual Steering - all you need is the steering shaft extension as mentioned above, the manual steering box & a pitman arm. I believe the pitman arm changed to one with a bigger hole (with power steering) for the "sector gear" (or something like that), but the manual boxes kept the older, smaller size. The Pitman arm is slightly different.
