Roy,
I do not have a source or dimensions for the 2.18 input but have another question for you........Are you sure which PSRU
that you have ?...........The early 2.18 version was designated "RD1A" and the later versions "RD1B" and the 2.85 version
"RD1C"............I have the "RD1C" 2.85 and could provide input shaft dimensions.........
Best Regards,
Kelly troyer