Too bad your ditchin the six,but for a custom radiator Ron Davis will make what you need.www.rondavisradiators.com ,or speedway motors might have some thing.
Look at aluminum mid-60's Mustang radiators, available on theBay for less than $200. Cured overheating problems in my '37 Plymouth that has a SBC.
ditchin the six because its been sitin in the desert for years with covers missing seized solid and i have a rebuilt sbc sitting on the floor in the garage
I bought a '38 Chevy business coupe about 2 months ago & it came with a Walker radiator. It cools very well with a warmed over 327 ci SBC in it.