Sorry but I don't agree. Handling an outboard motor is an awkward business at the best of times, even a small one. The clamp screws catch, the mounting bracket swivels out of alignment at the crucial moment etc.
The conditions you leave harbour in are not necessarily the conditions you find yourself in when it's an emergency.
A rib has a high bow and, therefore, windage. The motor lower unit will act as a sea anchor and it will be only a short time before the boat swings around and is floating with its stern to the weather. If the sea is anything above a force 3-4 then 2-3ft waves will be splashing onto the stern and the boat will be rocking and rolling. If they're Ribnet waves, they could be as big a 2.5mtrs
Mounting a motor whilst getting wet, balancing yourself, getting cold and, adding to that, the pressure of the moment and the possible unfolding drama as that outcrop of rocks gets ever closer, is not a situation you should put yourself into.
The auxiliary needs to be fueled and ready for use with the least possible hassle. Unclip the bracket, switch on the fuel, pump the bulb and start it is the maximum you should be looking at doing under stressful conditions.
I do agree that the tilt lock is unsuitable for supporting the motor while travelling. I'll draw you a simple bracket which could be easily made to support the leg of a small motor. No welding required.