What radiator to use???

A factory radiator with a new 3 core, a radiator shroud, and a good clutch fan should be all you need. If you've got a hot small block or a big block, then maybe go with a 26 inch from a b body. You'll have to open up the core support a little on both sides, but it'll fit. The trans cooler lines will bolt right up too. If you get an aftermarket, make sure that it has a trans cooler in the tank if you have an automatic transmission. Using an external cooler alone won't cut it.