Cooling problems

I have a 68 dart with a 470 . I'm in the process of getting it on the street . When I switched over from the 354 I left the 22" radiator in , it was fairly new . I had been using it with the 470
idling in the garage and about a two mile test trip. This week end I dropped the tranny pan and replaced it with an aluminum pan with plug. I put fresh fluid back in and let idle, I ran it in neutral and through the gears. I decided to take it out and check it out , same run as I had done before . By the time I got back the radiator was boiling over. It was over 90 degrees here. I wouldn't think the transmission would have something to do with that ? or coincidence.
Maybe should think about bigger radiator? Any ideas?