To avoid confusion, I added the OS 905 mount and NR Speed/13 engine pictures in a separate post here. Note the 44 mm spacing between beams. Limes are very useful when it comes to supporting engine mounts!
The last picture shows the dimensional drawing of the YS 60FR which I understand represents all 60 size classic pattern YS engines - YS FR & R
Classic short strokes and R & AR long strokes.
David