It is not particularly difficult to turn that Henry into a full auto. A machine shop is not neccessary. You need hand tools, and the method has been tested.
They took the lever guns in Australia, as well as pump actions, I think, because of precisely the issues you’ve raised. Of course, they accomplished nothing. Stupid people pass stupid laws.
I’ve got one cop video which shows the difference between aimed shots and spray/pray techniques and it’s pretty dramatic. From forty yards away firing a FAL rifle on full auto at four or five adversaries produced no hits which would produce major injuries while emptying the mag; four or five aimed shots produced kill shots on all adversaries while taking no more time. The impression I get is that full auto shooting should only be done with belt-fed weapons and you’re basically fighting WW-I when you do it even with the belt-fed weapons. The situation which calls for it rarely exists any more.