I don't know much about Isuzus really, but I've built a few engines and such and I'd say balance that flywheel/ring-gear setup otherwise you and a lot of drivetrain will be hating life. Machine shop should be able to take care of you no problem.

Also, I'm not sure how those ring-gears/flywheels are made, so I don't know if welding would be bad (heat)?!? Would hate to see it shatter apart on ya' once everything is put together. I think you're on the right path with small, low heat beads though. Can anyone comment on that? (Feel like I'm throwing in too much doubt here.)