Had a longish chat with Martin at Mad Biker Designs and I’m swinging towards a +4mm stroke engine using modified YPVS cylinders and a replacement head. Mainly because I can keep the YPVS system for a broader spread of power. Fair play to Martin as I had asked him to quote for a full Serval kit, he’s obviously not just about taking as much money as possible.
as mentioned in this thread, here is a dyno chart of a 385cc conversion I've just finished, this is a basic conversion running stock carbs and using the LC airbox, so limitations to some degree on the final power made, they make more with 30mm carbs and pods filters, I am on with one of them at the moment, for the meantime, the graph below will give you some idea
Seems like there are quite a lot using plus 4mm cranks for the build, I have decided to go that route with my own YPVS (after building my NS using a 475 kit) so what cranks does everyone use as there's a lot of price difference