Flexplate holes are slotted.. what should I do?

I'm putting my 4.1 NA Buick drivetrain back together and don't know what to do about the flexplate. The torque converter holes have become slotted from my neglect to tighten them enough on a previous rebuild, and the engine has a 50% race balance. I have a spare flexplate from a different engine, but it obviously does not have the same balance. Should I go ahead with the slotted one with the correct balance or should I swap the spare one on?
I'd weld up and grind the "oval" out of those holes. I doubt the weld and grind job will change the balance. You can probably tell which edge needs to be fixed, (the "clean" edge of the hole should look obvious) just weld up the mangled edge, grind, and redrill.