Thoughts on GG

I've been doing some bodysurfing and some bodypo riding (californiasurfcraft.com) and I've been enjoying myself. I have been thinking about trying to build a flexpoon using cork for the rail shape and floatation. That got me thinking deeply about flexspoon rails. What's going on there.
The history of the flexspoon is GG trimming material from his surfboard to make a kneeboard, and from his kneeboard to make a flexspoon. The name implies that the flexibility is the most important aspect, but I'm beginning to wonder. Flex certainly feels good when it's the right amount, but it's not as large a difference as the revolutionary surfing GG was doing back in the early 70's on his boards.
I'm not sure if hard, downturned rails existed prior to GG's flexspoon. Boards at the time were longboards that evolved from finless olo and paipo. When you are finless you use the rail to hold into the wave and avoid sliding the tail out. The roundness acts like drag as water flows over it. Once the fin came into play the round rails we no longer needed, but this wasn't recognized at the time. Rails with a hard transition from a flat bottom board break free the water wrapping around the rails and thereby free up the board from the wave. The result is speed and faster responsive turns.
When GG trimmed his kneeboard deck away to nothing, he was in effect getting rid of the round rail and making a hard rail. His surfing was tighter in the pocket, faster, and with greater turning ability. I had this same experience over the years when I moved from strictly classic longboard to shortboard and on to other variety of surfcraft. (And occasionally return to classic longboard.) Although it has taken me many years to develop the skill to take advantage of these design aspects.
So, if I'm going to make a flexspoon kneeboard, do I need it to flex? I want to mold off of and existing board and I have some options. The first option is a 5'8" kneeboard. I like the size but I've been told it's too small for me. Making a flexspoon off it would remove most of the flotation and it may become unusable as a kneeboard. Furthermore, the shape is quite different from a flexspoon with a central widespot, not being spoon shaped but more hard rails to the nose, and a quad-fin setup. The other option is a 6' GeeBee from Fineline. The template is very flexspoon, and the nose is spooned, but there is also belly through much of the board and the rails are 50/50 knife. It's also wide (for standing on) which I worry would be too wide for kneeboarding. Can I accommodate for that by making it more flexible? Is flexibility the answer, or just a small side benefit of the design. Will the belly in the board being used as the mold original be a problem? Benefit?
Gonna have to make something and answer my own questions.