I am not sure how long it has been installed. I would at say at least 40 years. When I was trying to get it out. The tranny tilted to the right, right as you look at the motor from the rear. The clutch moved with it as well as the motor. I could hear compression from the motor when it did. Surprised the heck out of me. Last thing I expected was the motor to be free and not frozen. I had to remove the motor to get the drive shaft off. There was no slack in the drive ling like there should be. I will keep working on it. After a few years, lots of heat, lots of WD-40, I might get lucky and get it off.