Just to point out - one reason why you don't see that many BP/BP-ZE engines on ITBs/bike carbs is that the standard inlet (and exhaust) manifolds aren't that bad at all. People have reported much smaller gains than those with ITBs on other engines. The UK based tuners seem to put ITBs at the bottom of the tuning list (after an aftermarket ECU, headwork/small increase in CR and cams).
Having said that, ITBs would be something I would consider doing (my engine build plans seemed to have escalated a fair bit from this time last year
). Phil, I would suggest that any design you also fits MX5s, you would be potentially limiting your market too much if you don't IMO.