radiator size in my 80 GMC

[cobinder]

I've put an old 49 International 1 ton body on a 80 GMC 3/4 ton 4/4 chassis. It has a 350 and now a NV4500 tranny . The chassis didn't have a radiator so I'm trying to figure out about how much fin area I need for a slightly pepped up 350. Is there a formula for this. I hate to guess and shell out for a custom radiator and not have it be cool enough.

Does anyone know what the fin area is of a manual trannied 350 in a 4/4?
how many cores?

Any help would be great

attached a pic of what a truck like mine looks like. Mines not done yet and is a 4/4 with a stepside bed, but you get the idea.
Jim