First, remove the exhaust collars or studs, whichever you have. This'll give you some more wiggle room. Cover the frame rails with tape/foam/cardboard if you're worried about scratches.
Assuming the frame is upright and firmly supported, the engine needs to come up about an inch in the front, and a few inches in the back. In other words it needs to get lifted and tilted forward at the same time.
The engine will then slide directly to the right and out of the frame. Note that the rear of the engine will JUST clear the gusseting at the rear right of the engine, and JUST clear the front rail of the frame. Any twisting or leaning will get you hung up.
I like to straddle the frame, leaning forward over the backbone, and reach down and grab the motor from both sides, by the alternator cover and under the points cover. when you lift the motor it'll want to lean forward naturally from the weight of the cylinders and head. Edge the motor out to the right a little at a time.
When lifting the frame off of the motor, the motor still has to take the same "path" as above in order to exit the frame.
mystic_1