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

As a complete engine, the '62 and newer 318 A engine will interchange with a 318 LA engine with the usual notes.....auto/manual crank pilot hole machining; exhaust pipes, water pump type, brackets, etc. Without knowing the exact years and options of both engines, it's hard to tell what all you'll need to do. They bolt up to the transmission. Just make sure the correct flex plate is used. They swap over, it's just the A engines all have 727's behind them and most LA 318's have 904's. Some flex plates have a different convertor bolt circle diameter.