A518 Flex Plate Help???

I really doubt that you would notice the difference in 2500 or 2800.
If there was I'd be buying one and selling the one I have. but It's not worth all the work and xpense for such a little gain.
If yours is a 73 cast crank like you said earlier, then yes the 10235 is the one I'd get along with a neutral converter.

I haven't dealt with nor do I know any good or bad about PATC's converters. I did buy their vacuum disengage kit for when you floor it. It works good but you can just as easily reach over and flip off a switch.
By the way I'm runnin 3.91s and 2300rpm at 65.

TCI can charge a little more for their Name recognition, and maybe deserve it, I dont know. They were the only ones I found that had a higher stall lockup back then.
I was on my own then, didn't know about FABO.