Professional products balancer: which weight for magnum

Then you should ask him for clarification on what the different weight applications are. If he designed it, what are the correct applications?
If the later LA 360s have a lighter roatating weight than earlier LA 360s, then that puts them right in line with Magnum 360s, or at least close enough that it works fine for street apllications.
When in doubt, have the rotating assembly balanced.