converting manual steering to power steering

You have to cut the steering shaft maybe 2" shorter to fit the power gear-box, and drill a hole for the link rod. Most people go the other way (need an extender for manual box to power steering shaft), so you might swap with someone to not molest factory parts. You could also swap the whole steering column, but many disassemble theirs to restore anyway.

An early A would have the TRW pump. It looks like the later Federal pump but different brackets and fittings. The TRW pump for C-body has a larger shaft so pulleys don't interchange, and a C-body pulley has a different offset to not line up with the crank pulley (how would I know?). I vaguely recall B-body were the same as A. The TRW pump brackets only fit the early cast-iron water pump. The Saginaw gearbox is said more efficient and is much easier to source (GM). If there are brackets to fit the cast-iron water pump, Bouchillon Performance Engineering may have them.

You need the early power gearbox. Around 1973, the sector shaft got larger in A and B-body (same as C-body) so your Pitman arm wouldn't fit. The inlet and outlet fittings on the gearboxes vary between the three power steering pumps. You can interchange the bolt-on in and out housings to fit or adapt hose sizes inline. The A and B-body factory H.P. hose often had an inline coupler to change sizes. My C-body hose had the same fittings but a custom end adapter to change the flare size. Later setups used O-ring H.P. fittings at pump and gearbox. I've got several power gearboxes stored, but shipping for individuals is outrageous for anything but small parts.