The 318 in my car right now is wasted. I have another one that i can build or there is the possibility i can get a 360 for roughly $400 (needs to be rebuilt). Do you think i should just leave the 318 stock, drop that in and build a 360 instead?
IMO, this is the best way to go. Build a 360 on the side for later. When your ready, make the swap.
The 318 can be the test bed for fitments, for a verity of parts. Intake, carb and air cleaner, headers and exhaust can all be swapped over to the 360 when the time comes. While your "Testing" the parts for fit, HP will increase for the 318.
Now weather you do a 318 or a 360 for a final engine, that is your choice. I myself would do the 360. But build it on the side. You can even have it dyno'd before you drop it in. This way, you can work out any bugs, tune for max power and mileage. The engine will be broken in and ready to rock and roll.
Just remember that the 360 is an external balanced engine and the 318 is a internal balanced engine. If the 360 remains a external balanced engine, B&M sell a flex plate for cheap that will allow you to use the internal balanced converter without issue.