Went digging in the Hollander Interchange books I have that cover '54 - '66, Carl.
The '55 and '56 Mercs used the same T-85s with R-11 overdrive units.
'55 Mercs were 6 volt, so I guess the overdrive relay and governor is different from that used on the 12 volt '56 Mercs.
Hope this helps.
NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York