Im not sure on the trans as you can get a brand new one from summit for like 1300$ that already has the usual performance mods installed.
https://www.summitracing.com/parts/hup-34-1b/overview/
Here is a 67 400 block already magnafluxed. Granted it does have a sleeve, which you could use as a bargaining chip...
https://www.ebay.com/itm/pontiac-400...-/273870527809
Are you looking to then sell the drivetrain once you purchase the car? I think 1500 even with 42K original miles is pretty high. I have had people pay me to take 326's away.
Any pictures of the project car?