But a 55-pound engine is too heavy for me to mount one-handed. 30-pounds OK.

The image below shows the Forespar MotorMate crane I use for my 59-pound 9.8 2-stroke Nissan. I stow the dinghy on a side-net, and after launching -- maneuver it to the aft rail of the center hull where we lower the motor and position it while hanging from the crane. Holding the dinghy stern-to the mother boat while the lift is used by my wife can be a bit of a timing challenge in 25-knot winds and choppy conditions, and is best done as a two-person job.

I expect it to be easier (and a one person job) to tie the dinghy close alongside, then pick up the 30-pound motor from the rail, and carry it with one hand to the side of the boat where I can lower it by one hand (using a lifting strap) onto the dinghy, while still having a hand free to steady myself or the dinghy. Have yet to find out how well it works in practice. Maybe we'll end up using the MotorMate with the lighter engine too.