So, James came over last night and we fixed the stripped stud.
Exhaust ports and oil cooler were covered to avoid tragedy:
We drilled the old threads out by hand - due to clearance issues with the oil cooler, we couldn't use a tap wrench:
Next was to counterbore the hole:
Tapping:
Unfortunately, despite doing everything without power tools and following the old hole as best as possible, our threads ended up slightly off. I don't believe it's enough to cause a problem with fitting the exhaust manifold, but it was enough to make the Time-Sert not seat completely flush. I had to open the hole in the exhaust gasket a little to avoid it getting pushed up by the imperfectly seated shoulder. I'm not happy about this, but other than machining a tool to ensure a perfect 90° angle and then re-doing it with a Big-Sert, there's not much I can do. We didn't poke a hole anywhere we shouldn't have (yay for intact water jackets), so absolute worst-case scenario means I just get another exhaust manifold leak. I think it'll be fine, though. I'll fix it once and for all when I put a built head on.
I may postpone replacing the square bushing thing, since I'm reading that people have had starter mounting bolts break or starters come apart during removal (yay for old cars). I've also found a zip-tie holding something together down there...and since everything has been working for three years, it may be wiser to fix this properly
after I drive it to AZ. I'm leaving in 3 weeks and I can't really afford the time to fix problems that I may inadvertently create.