I wouldn't get too carried away driveline, not worth it without the original engine plus boring. I own the oldest known surviving V8 HK GTS, its original engine has gone so I ripped out the Powerglide, banjo and the whole front end. Car is repaired and painted as per original but its now got a 9" and a Rodtech front end with power steering. Giving it an injected 305 with TH350C to get it sorted and later will get a stroked 350 (377ci). All changeable back but no interest for me to do that. Don't waste your time on a 10-bolt if its not there now, will cost too much. I'd use the 9" but if you want a Salisbury and it was originally a Salisbury (as in has the clearance hump for a 12-bolt) buy a 12-bolt. You will never break it. Stick with the 327 unless an original Pagewood HK 307 falls into your lap, not worth the effort.

Preserve if they are original. Once they are heavily changed, lost their engines etc. I cannot see the point. Especially on a lower spec car, its a GTS not a GTS327. As I said make it look original exterior and inside, but there is no good reason to make it original mechanically if you can do it without affecting the integrity of the car. I'm not promoting making it heavily modified like an LS, just bolt in stuff like engine, box, diff, steering and brakes. The amount of $ you'd spend trying to make it all original 307, Powerglide and 10-bolt would cost more than having a nice 327 or 350, 3spd auto and 9" with HQ brakes. That is the track I've taken with my HK GTS. It has the most original HK driveline in it you've ever seen from a totally original radiator, 307, Powerglide and banjo plus original exhaust. But none of it is original to the car, so why put up with it? The whole driveline came out of a mint HK Brougham with maybe 25,000 miles on it.

Hey Wagon Dan/HK1837 , been watching and appreciate the differing views, totally seeing both sides, the purist in me says Wagon Dan all the way, and my right foot at full throttle says HK1837 my thoughts on where i was going 5 days ago and now today couldnt be more different, will certainly be going factory black and the 14x interior, 0bvioudly black will require a lot of panel work , would like to go manual transmission, have a 327 so will use that, would b good over time to accumulate diff and 307 engine / rebuilt powerglide, all bolt in and in years to come if sold or what have you someone or next care taker can pic his poison,
Ask me tomorrow will be different again, Dio mio,
Certainly appreciate you both🙌🙌