Nice looking build. Reminds me of this future-but-never-going-to-happen 3-500Z push-pull monster amp. I mean, it's not a real tube unless it needs forced-air cooling, right?
I've always wanted to build a monster push-pull amp with transmitting tubes, but the OPT is really a barrier. Even an 811A or 572B (572B is pretty much a beefed up 811A), the plate voltage would be 1200v or so. My thinking is that the OPT would need to be insulated for at least twice that. I assume that the output transformer the OP used was custom wound. I'd be interested in getting more information on it.