I was in the same boat you are now. Knees around my ears and couldn’t get my feet vertical enough to brace myself in the seat. Unfortunately, I am so tall, that even with a front porch my feet are still pitched forward a bit. I make it work.
As far as what is available, Mike Jones at DKC advised me that the CRG is universal. Personally I had one custom made. Like you I wasn’t sure about the fitment of the CRG on an OTK, because the OTK front hoop and pedal mounts use an unusual tapered tube that a non-tapered tube would flop around on. Unless you could find or make some kind of insert that would fill the gap of the taper, then it could work.
I worked with a guy that races Dirt Stock Cars and asked if he knew a cage builder. He was able to recommend a guy in the area that I hired to make a custom front porch. He was able to get the pedals 4 inches further out and allow me to get the seat back in the tuning window. In retrospect, I should have had him make it a little longer to get the pedals 6 inches out from factory. I have some pic posted on another thread.