You can buy a bolt in aluminun rad from Tiger Auto in Dayton OH or get yours recored with a brass rad at your local rad shop. Ask for a core by Windsor, Sunbeam rad # 128366 or equivelent. Virtually any modern brass rad works fine. Keep it 2″ or less thick. Alumnum can work as good as brass, not better.
Basic cooling “recommendations”
Use a Derale 317015 fan (DO NOT TRIM, raise/move eng), block horn holes, and space between rad and crossmember, use a fan shroud.