which engine in my 74 swinger

I'd run the hemi, I'm sure it wouldn't take much to hop it up. I'm not talking money, since Hemi stuff is more expensive. Good valve job, cam and springs, modern 4 barrel carb? Should get decent milage and wind up quick and high. But only if you were going to keep it. If you might sell it, any Mopar V8 will go fast...