IMHO your best best would be to find a used 2 piece rear main seal 350 and a TH350 trans. Also a good set of used vortec heads with appropriate intake, carb… Basically if your looking to do this on a budget then you should get on craigslist see what you can find and hit the swap meets come spring time. 350 motors and trans are very common just check the bellhousing area of the trans for stress cracks. Easy enough to have welded, but some thing to watch for. The good thing about GM stuff is for the most part it all works together.