Unfortunately, not that I've heard of. In fact, I've never ran across anyone else that had their factory flex plate balanced. They all use either B&M flex plate, weighted converter, or had the assembly balanced during rebuild.
I did this about 20 years ago, when I bought a TCI converter, then went from a 340 to a 360. I asked the machine shop I was using what they could do with my flex plate, and they said "no problem". Man was that 360 smooth.... weird, even with a rough idle cam it was smooth. you could hear the "thump-a-thumpity-thump, but that motor was dead still. They got me 45 bucks back then, and I thought that was a good deal.
