What needs to be done to go from trs to a speedmaster III. Will the transom have to be recut or is cut out the same? Will the transom have to be filled? How much does it usually cost to fill a transom drive cut out and recut it? Thanks

Cut transom, swap TRS tailstock for a SSM tailstock on trans, move engines back a few inches.....

Will the transom hole from the trs need filled first or just need some more cutting?

The SSM cutout is bigger I am pretty sure. You would want to plug the old mounting holes from the TRS though. My boat was a TRS boat originally, now has SSM drives, but that was done prior to me owning it. Couple buddies older cigs were converted too back in the day.

Different shape cut out. Better off filling and recut. You can use a new transom gasket as a template