318 or 360? That is my question...

A 360 engine should fit where the 318 was, externally they are the same.

Early LA 360 engines have larger ports and valves than 318 engines.

Basically everything is interchangeable between a LA 318 and LA 360 engine EXCEPT engine block, crankshaft, main bearings, harmonic balancer and pistons.

If you need spend money on the block or crank it might be worth looking for a 360 engine to begin with. Your budget will probably decide for you!