Test fitted the radiator tonight. Its an aluminum unit of unknown origin- it was installed in the 66 Dart wagon donor car.
It mounts very close to the 4 blade fan due to the 1/2" spacer needed to clear the fan from the PS pulley & belt.
Tonight I noticed a previously unknown detail of the radiator support. The radiator mounting flanges are different on each side. Originally a 273 4speed car, the drivers side flange is 3/8" closer to the motor than the passenger side. The radiator mounts a bit crooked as its mounting flanges are symmetrical.
I dont weld aluminum, so I'm considering trimming the radiator flanges so as to mount it to the front of the radiator support on the drivers side to even it out a tiny bit.
Trimmed the driver side radiator mounting flange so as to bolt it to the front side of the radiator support. Now its cockeyed in the other direction, but closer to symmetrical and fan clearance is good.
Also started rust repair on the replacement fender.