I have seen several people use the Speed Engineering headers and motor mount adapters.
https://www.speed-engineering.com/ls...2-ls3-ls6.html
I recently bought a radiator from Superior for my '51 and I'm really happy with it. So I will buy from them again for my '64 suburban. They're US made and do LS swap radiators.
http://www.wwwsuperiorradiator.com/1...7_chevy_trucks