An engine mounting bolt/nut torque is recommended to ensure that engines remain secure on the transom. The transom mounting bolts/nuts should be able to hold the recommended torque of the fasteners listed below without the transom yielding or cracking. If the transom yields or cracks under the torque of the transom bolts/nuts, the transom must be strengthened or the load carrying area increased. Always use manufacturer supplied fasteners.8/9.9 FourStroke non‑power trim engine with ¼" bolt7 lb. ft .8/9.9 FourStroke power trim models with M8 bolt10 lb. ft .15 FourStroke with 5/16" bolt25 lb. ft. 25 EFI FourStroke with M8 bolt10 lb. ft .25/30 EFI FourStroke with M12 bolt52 lb. ft. Outboards 40 and above with ½" bolt55 lb. f
this is right from the merc manual
Outboard mounting locknuts and bolts – standard boat transom 55 foot pounds
Outboard mounting locknuts and bolts – metal lift plates and setback brackets 90 foot pounds
the 90 pounds torque would b mounting the motor to a jack plate.