273 for early A

Consider Rhoads leak-down lifters. It will make it run better at low rpm, with more vacuum yet give full lift at higher rpm. Better cruising, mileage, and less emissions. Unless you like that stumbling "race car" idle that some seem to like (not me, I'm an engineer). I put a hydraulic cam (RV Torker) in my 65 Dart 273 w/ Rhoads. You can use the stock adjustable rockers if you buy shorter 340 TA pushrods (ball & cup). The adjustments let you set the lifter pre-load perfectly. Unless you have your heart set on a carburetor, I would buy a throttle-body EFI. They are now <$1000 even with self-learning, while carb prices keep rising. You should save just in the better mileage. Good luck.