The manifold nuts were about the nightmare I expected. None broke (but I did break one on the divorced choke thermostat

The manifold studs used to be available (and cheap) through Silver Seal but they no longer have them. Has anyone found anywhere to get them at in bulk? I usually bough 3 or 4 sets at a time.

I got my most recent ones a year ago from an old school parts store whose parts counter was a huge dorman cabinet.
Next choice would be to hit up McMaster Carr.

Groan. You might want to take the opportunity to un-handcuff yourself from the '70-'72 exhaust manifold, and at the same time greatly increase the odds that your R&R job will wind up tight/unleaky and with everything working for a long time.

Specifically, the '70-'72 manifolds have an open "stove" (hole directly into the inside of the manifold) at the top of the № 5 runner. This is sealed (kindasorta, not very well) by a stamped sheetmetal cup that fits into the hole, with a (no longer available) gasket around its perimeter. On top of this cup is bolted the choke thermostat. If you are bound and determined to run this manifold, and there's any kind of a fault with or near the choke—doesn't work quite correctly, rod all tweaked and bent, rusty AF, exhaust leaks, etc—fabricate a blockoff plate and cut a suitable gasket for it, then plop a № 1231 electric choke kit on and be permanently done with choke problems.

Given its age, this manifold is likely warped, and there's a high likelihood of cracks and/or heat control valve faults as well, so unless you have no budget, you're best off installing a carefully chosen new exhaust manifold. Good idea to put in all new manifold studs while you are at it; it can easily save you multiple kinds of aggravation and badness later on. Find hardware and mounting-technique info here and here.

It is very much worth your while to get the good gaskets for the manifolds-to-head, intake-to-exhaust, and exhaust-to-headpipe junctions.

That's a '73-up manifold set (intake + exhaust), so you avoid the choke-cup problems mentioned. Does the heat control valve work? You'd still want the № 1231 electric choke.