Gnarls right mig.,I think without checking in the books that you went from a 1:50 ratio to a 1:43, that would explain your rpm.
The drive coupler where going to use is the standard merc BBC.It bolts on the flywheel like a clutch,so some drilling of the ford flywheel is possible.The merc. and the omc both have the same input shaft so there is no problem there. The bellhousing does not have a big enough center so it has to be cut and rewelded to accomadate the merc part.
As for any other problems , weve had none, there a really good unit.
Johnc-I'll put up a new post tomarrow or sat. with engine specs,kinda on the run now ,thanks for the interest.
GOTTA GO NG