I've wondered how much alignment changes between engine off and engine putting full torque to the drive, transom and engine mounts anyway...
Should be zero difference. Straight inboards are aligned with engines off . So a 36" boat with twin 502's when taking off is going to develop gobs of torque, the cutlass bearing ( a 6" long plastic sleeve in the prop shaft struts ) takes all torque. If it's off by hundredeth's of a fraction , you will feel it . The engine mounts have extremely hard rubber in them and really just isolate the engine vibration from the stringers ,which keeps the rest of the boat from any vibration . In a I/O the transom should have zero flex as well , regardless of torque transferd through it . Usually if it goes out of alignment its because of poor construction, as in weak stringers , lag bolts used to secure the engine mounts to the stringers or water intrusion in the transom or stringers . Engine mounts in cars are different and you may see the engine rise a bit when torque is applied , but the drive system is designed to flex more or less through the drive shafts universal joints .
