The TSS RS500 2 stroke twin the boys down in Australia have been working on has been installed in an an Aprilia chassis as intended and fired up. It looks like it fits perfectly and they have a short video of the bike. It sounds good. Steve adds:
The motor fits in there like it was always designed to do - in fact I have a consipiracy theory that Aprilia initially had intended to buy a parallel-twin reverse-cylinder engine from Yamaha but the deal fell through, leaving them no choice but to go for the RGV engine. Because when you see how perfectly the big 500cc twin fits inside the frame spars, this is the inescapable conclusion you come to. The barrels and head come on and off without so much as touching the sides; there is far more room for removing barrels than in the case of the engine in the original RZ350.
Photo and video below:
Link: Two Stroke Shop