Its a lot harder (and a lot more expensive) to put a 440 (or any big block) in where a 318 now rests. The big blocks made a lot more power, and if you could keep your foot out of the throttle, actually got better (or the same) gas mileage most of the time, but those days are gone, the parts are getting harder to come by. The 318 works well in those old power wagons.

I think I would probably start by replacing all the steel and rubber pieces in the fuel line(s) between the tank and the car (both lines if it has a return line). Those old steel line would get rust pinholes up near the tank and would suck both fuel and air causing problems that are hard to see or find. If it has been sitting, I would also plan on replacing all the brake steel lines and rubber hoses (and probably calipers and wheel cylinders) as well. If the firewall or brake booster is wet behind/below the master cylinder, plan on replacing it as well. Those rubber seals and hoses don't survive well just sitting, and the steel lines are all rust magnets. Just my experience.