Boy that's a NICE lookin' little car!! I'm pretty much with everybody else-find yourself a decent running 318. You should be able to pick one up for 3-400
I'm putting an "interim" 360 and 727 in my old 67 Dart. I bought a 77 Dodge van for 350 and junked it out
One caveat --I'm not sure of. Didn't the older engines have a smaller torque converter nose? Not sure what year they changed that.