273 - 318 swap

As long as they use the same vintage water pump and timing chain cover.

The 64 - 69 with the cast iron water pump.

If the 318 is a 70 or later you can put the timing chain cover and cast iron water pump on it. You will just have to keep the 318's vibration damper and mark where tdc is on the damper in relation to the older timing chain cover (they will be 90° off).

No problem.