The easiest way to upgrade the 318 is with early and well prep'd bowl ported 360 heads milled to keep the compression up, RPM, headers into a 2-1/2 pipe, a good distributor and ignition along with the cam of your choice. Add the proper stall and rear gears, you'll have a good runner for cheap. The timing gear upgrade that 318willrun suggested is an excellent idea. Heck! Since you have the front off of the engine anyway! Ya might as well do it!