If I recall correctly, when they released the C model TT500, you could get them with a lighting kit fitted and a small speedo on the fork leg, sort of like the TYs. I believe in some states they could be registered in that form... It wasn't hard to do that in any case - I had a PP headlight/plate plus a TY175 taillight on my TT500F, along with a simple brake switch, on/off switch and a little mirror and got it rego'd like that.
It may even be still registered as my mate still has the bike...