I wouldn't even think about lying to an insurance company. If you should have an accident on a transit, where that insurance would be applicable, they can say that you didn't advise them of the mods to the car and you would, in effect, have no insurance -- they would go after you for the money they had to pay out.

Re street legal, if you watch WRC rallies, you'll note that sometimes they show a clip of how they are checking the cars to be street-legal -- brake lights, turn signals, mirrors, etc. -- the things that all cars must have on the street. The performance stuff is covered under the mandatory tech inspections (and logbook).
Check out the MCO forums -- there is info on a company that is setting up insurance for cars that are difficult to insure. I think it was on a Solo II forum, but there's lots of angst being expressed about insurance so do a bit of browsing there.
Good luck!!
Jeannie