Where to buy rebuilt engine?

as far as 318's note that anything you buy isn't going to have the same manifold bolt size and angle in the heads, so you'll need a manifold, or to re use your 273 heads. also, the crank pilot is larger so you'll need an adapter for your smaller hub torque converter (not a big deal).

i have a complete 273 that's a great runner-- pulled from my 68 dart that i'm doing a big block swap on.

shoot me a PM if interested.