Where to buy rebuilt engine?

Just remember if you go 318 you will need a 318 flywheel or flexplate and if it's automatic you will need the bushing for the back of the crank for the torque converter hub as all 273s used small hub cranks and all 318s use large hub cranks.
There's a shop in town that will build the early convertor with a late snout to fit the larger crank register