need help deciding a motor

My Opinion, if the 273 isnt seized, put it in, and spend a few bucks to get it running in the car, then you have something to putter around in until you decide which other route you want to go. If its a HiPerf 273, and you arent planning to Drag Race the dart, it might do you well enough.

Then you can work on the resto, drive it, and save for the big hp it sounds like you want.