The plate started as a piece of 6061 Aluminum 14"x 14"x 1.25" thick. First operation was to water-jet the outside profile and inside clutch-plate clearance hole. The known location mounting holes were also put in 1mm undersized. The second operation shown above was to remove 0.25" from teh motor side to create the raised boss that can be seen in the center. This boss aligned the motor during install. The plate then went to another shop with a large lathe to finish the boss accurately. Then to a fourth location to drill and tap all the holes.
Adapter plate being aligned to the transmission.
At the fourth shop we used the center boss to center the plate on the transmission and then bolted, drilled, and inserted two pins to permanently align the plate to the transmission input shaft. We got the plate aligned to ±0.00125" TIR.