You still have a SBC using a BPE 383 or 396. What people are referring to as a "BB" radiator is not what you want as the top outlet is angled on a BB radiator which is 23" wide. You want the 23" SB (it was for SBC w/AC), vs the stock 21" radiator.
The stock 21" fan shroud would "work" on the SBC 23" but you would have to make some simple metal tabs attached to the shroud (DS pic) to extend to reach the lower clip of a 23" (better IMHO) radiator...or buy the OER SBC w/AC fan shroud from Summit (what I have).
Cold Case is a sponsor here and their radiator is a 1 1/4" x 2 row aluminum. I and many others have one. Contact the people noted earlier (PM) for current $.
I would also install the top close out panel, use a 18"-7 blade with fan clutch mechanical fan. Electric fan setup will cost considerably more for the system that actually works but that rabbit hole can get deep and $ but necessary if you insist on a serpentine belt system.
21" shroud on a 23" SBC stock radiator
23" SBC w/AC (I don't have AC) shroud on the 23" CC SBC radiator with closeout panel
23" CC radiator
Regardless of radiator size or brand, IMHO get a "coolant recovery" tank. Use the OER 75 Nova tank available at places like Summit. Just drill 1 hole in inner fender (forward of body ground wire) lip to install. I chose to route the hose along core support to inner fender and around to attach to tank nipple. Plug and play install but you need to remove battery to install. Cap is sold separate.
I have a BPE 355.