whats the difference...318 SB and 318 Wide block?

I'm assuming he has a 318 Polyspherical engine. Sometimes called a 318 poly. They were also called the A engine. The later style 273, 318, 340, & 360 engines were called LA engines but I'm pretty surethat both A and LA engines all used the same transmission bell housing pattern. Several other parts will also swap between the motors. I'm not positive that the motor mounts between the older 318 & the newer one are the same but I think they are.