They can be a pain to get off sometimes if the coupler has rusted on the input shaft. Usually if you wiggle and pull it will break loose. Try tapping on the case with a hammer while pulling on the motor.
Had me worried TOO! That motor was a BEAR to get off the rear end! The housing came off and the rest of the motor stayed, I thought I had broke the motor at 1st. I am GLAD IT's OFF! Sending it to PQ this Morning!
Paint the parts with anti seize compound available in auto parts stores, I use the stuff any time I think disassembly could be a problem in the future. I'm too damn old for the intense heat, profanity and big hammers routine. LOL!