Great project. Before you start, a thought for you... the ns400 engine fits into an RGV or RS Aprilia frame like it was made for it. Also, think about fitting some 1983 CR125 cylinders to the NS400 engine. I did it a few years back, as the the limiting factor on good power was the reed block size... the CR is 33% bigger than tiny ns400 cylinders. A full 500 was good for 95bhp.

Good luck

Dan