It sounds like even the Japanese had some dimensional issues with their products. I intend to solve this problem and figure out the dimensional requirements "spinner back" for the more popular classic 60 size engines. In the case of beam hardwood mounts like were used in many of the MK designs, this should be very straight forward. The metal plates are drilled at a standard width on the beam and the location of the mount bolts are placed according to where the nose ring is located. A dual purpose plate like the IM you're describing Matt, seems unnecessary given the cost of sheet steel and even if they were properly drilled we've already established that a combined 20 and 25 mm spacing leaves too little clearance for comfort between different brand engines (e.g., YS & NR).
The dimensional stuff will work equally well for beam aluminum hard mounts as for hardwood/metal plate systems. The vertical "backplate" mount systems are easier to deal with since putting the thrust washer where it needs to go is a matter of spacing the fixed FW with some ply spacers. Using 1/8", 1/16" and 1/32" ply spacers one can fine tune the spinner position. The main problem arises when one swaps out a modern short engine such as a NR or YS for a vintage engine such as a Rossi, OPS or Picco. On slide mounts this can usually be addressed but on typical FW mounts (Al or FRP) or backplate mount this is not quite straight forward as the space in the engine bay is often not sufficient unless planned for a priori.
David
Last edited by doxilia; 11-09-2014 at 10:32 AM.