I did that back in the early 1980s in a 340 block, that motor is still running. I used a Speed Pro 360 forged race piston(13.0 to 1 comp) and cut the tops off, had the crank assembly nuetral balanced and put it in the car The thing about the 318 bore is that it may end up needing a custom piston made for that stroke, which is of course is more money than a standard off the shelf piston another option is to offset grind the 360 rod journas to big journal SB Chevy rod size, use aftermarket Chevy H or I beam 6.25 long steel rods and increase the stroke to make a bigger C.I. motor, which will end up making a lot of torque