The MID is definitely for Midland. Don't know what the B is for. Have seen others with A so it stands for something.
The Midland tractors are easy to identify because they are the only ones to use a single oval tube for the handle bars as far as I know. If you could find the serial number on the engine you can date it here
Wisconsin Motors | Engine Repair Support & FAQ
They also have the parts lists.
Garry, I don't have a I.D. tag on the engine, I hope that maybe the info from the mag and carb. will help us id the engine..I do believe that it's a Wisconsin. Thanks for all the help.