The diffrence in ballance is in the rods/pistons. La and magnum use the same crankshaft. so you really need to find out what rods and pistons are used to get the proper damper and flex/flywheel
Agreed. That's why he needs to contact the rebuilder and find out what he actually has in his engine and what the balance is.
OP- "even if the engine has magnum heads"? It doesn't sound like you're sure if you have Magnum heads or not...? If the rockers are shaft mounted, they are LA. If stud mounted, they're Magnum. Or just count the valve cover bolts- LA=5, Magnum=10