26" radiator in my 1974 360 dart sport, this came with the car. Should i be running a good 22" radiator?

No harm will come from running a 26" radiator in front of a radiator support that has an opening for a 22" radiator. I've had a 26" radiator in my '74 Duster since I converted it to a v8 from the original /6, and it had a 22" radiator from the factory. Yes, you lose a little bit of airflow at driving speeds, but typically if you're going more than 25 mph you shouldn't have an airflow issue anyway. And at idle, with a good fan shroud the fan will pull air across the entire core anyway. And typically idle or slow speed driving is the problem, and the fan is doing all the work then.

I'd be more concerned about the fact that the radiator in there appears to be a single core. I mean seriously, it's barely half the width of the radiator cap. Definitely not anything factory for one of these cars, they were all at least 2 row and that makes them at least as wide as the cap.