I got lucky with the radiator as it came with the car when I bought it. It is a "927" unit:
""Large 26" Radiator core from a Mopar B-Body Road Runner, Charger or Super Bee with a 340 or 318 with A/C. This has the integral transmission cooler, but was used for both manual and automatic cars. Chrysler part no. 3673927.""
1970 YO7 A66 [Canadian Export] F8 Challenger 340 (Currently in shop for stroker assy.)