The design of the RG 500 engine is more than 20 years old now. Among the other things, the 56x50 dimensions were abandoned by all manufacturers. Those who tried to keep with it, lost the competition. All modern design engines are 54x54 based, and all the latest development of transfer ports etc. etc. is based on that.  I don't want to reinvent the wheel, nor I think I alone in my spare time could do better than famous companies with billion dollars budgets and huge engineering teams could do in twenty years full time work.   The most logical thing, in my opinion, is to build 54.4 mm stroke cranks and then adopt already made, MODERN, 54x54.4 cylinders. Plain and simple.