Although the 'Zephyr' guard fits exactly between the suspension sliders, that may not be such a good thing as the brake hoses go between the guard and the leg on the standard bike. maybe a 'racing' guard that is 1/2" narrower would be neater, spaced out to give room for the hoses.
The fiberglass guy said that If I gave him my tank-seat unit he'd take a mould off and make some more. I don't really want to destroy the patina on mine, though. They are available already and I can see that the cost, taking into account sealing against ethanolol and a filler-cap, tap bosses etc might not be too competitive, not to mention product liability of petrol tanks etc. If you really want one, let me know and I'll do some investigating.