Been thinking about this. An engine stand has 4 arms that are adjustable to various motor patterns. I have a 4 wheel one myself. Don't take this the wrong way, but what is the problem with using the stand? A specific motor stays on a stand for a long time. You don't switch motors every day or week. What does an adapter save you? You have to undo the adaptor and store it away with extra motor bolts and washers?
You hold the motor up in the air with a cherry picker, roll the stand up and bolt. 15 minutes. I don't fiddle. The washers stay on the stand with a temp nut. Weld on/bolt on a stick-up bolt/stud to store washers.

Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn