Odd shape emblem...Rickenbocker?? That's spelled Rong! Edit...Rickenbacker is right, or at least better.
the shape of the radiator will depend on the positioning of the shell, its mounting, fan clearance, etc, etc. Better to get the final engine position settled and the grill shell positioned before selecting a radiator. That said, a typical starting point is the first gen Mustang.
Rickenbacker is correct (I checked) here is a page with some to look at I think I saw at least one with that rad shell. https://www.google.com/search?q=ric...X&ved=0CCoQsARqFQoTCKnd-K7x08gCFYiTDQodASQFqA If we had the dims we could better tell what would fit and be cheap(ish)
18 x 24 x 4 I know it's gonna be "modified" ...I was thinking of visiting the tractor junk yard for the radiator ...will a tractor radiator even cool a small block chevy?