Ensure the engine mounts can be adjusted, [ no heavy rust on threads ] & are not fatigued, sagging, or oil soaked. If the mounts are over 10 years old, they are suspect. Ensure they are firmly attached to the stringers.

The stud should be vertical, not canted to one side. This puts a side load on that mount & accelerates wear, it also makes alignment difficult. Disconnect the couplers by bolt removal & seperate them - note any rough misalignment.

Clean the mating surfaces of the couplers of any rust. Adjust the engine / trans mounts to get the couplers in the same plane, by eye. This is the rough alignment. You may discover the mounts run out of adjustment before the engine is aligned. In this case, I would suggest it be evaluated by a mechanic, as the engine mount / strut system will have to be rebuilt.

Now slide the shaft coupler fwd to contact the trans coupler. They should mate evenly - just imagine both couplers are pistons in the same cylinder - contact should be made flat & square - check with a straightedge around the couplers for a concentric fit.

Now for the final adjustment - get comfy, & insert a .004" feeler gauge between the couplers. Check for even fit all around the coupler circumfrence. Adjust the engine mounts to this standard, while maintaining the couplers inside the imaginary cylinder. Take your time, it's not easy!

When done, torque down the engine mount lock nuts & recheck alignment. Now re-install the coupler bolts using new lock washers - NOTE - these bolts are fine thread, for strength. A jumper wire between opposite coupler bolts - 10 gauge - can be used to bond the prop shaft. Concider installing a "Drivesaver" or other flexible unit between the couplers to compensate for the minor misalignment that happens underway

Joe D