Yep, the original GM combo isn't going to be cheap or easy to improve in my opinion... a 700R automatic is the only thing I'd personally even consider..
There's a guy local to me, Chevy 2 Only Nova Parts, he's been at it for decades.. I haven't seen him lately but at one time he had any, and everything for those cars.
I was trying to remember the name of the fiberglass hood I'd bought for a truck many years ago... yes Harwood!
Those springs were extra but they worked perfectly.
If it has a clean title...
I don't know about Virginia, but here in KY it's become very difficult to title a vehicle like that if a title can't be found.
My truck had rust on one side of the frame there.
LMC has both the outer & inner spring perches, the frame can be repaired there when they're out of the way.
I brought that dealer point up in another thread, I believe it was about mirrors.
Dealers put on all kinds of things on vehicles in those days, lots of folks probably thought they were "factory"
The 40-40 was the one to get... but that was a long time ago...
My pal has two of them they both need repair/parts but it isn't economical because they won't do the majority of today's wheels.