I thought of doing my old Parilla , tt-25 and ss-21 rotary engines as a siameese , with reed in front and rotary in back, regular pipe on back and an enduro straight pipe in front.
I like Hilton's set-up. Both belt drives were on the right (looking from the rear). This meant the engines were setup the same. If you had a spare engine, it could go in either spot. I am about to own a set. I hope it will be able to compete with that awesome Jawa power we are all about to see more of.
I can't remember how many of those Hilton had his CNC shop make but it was a few. I can't remember if any were for Yamahas.