Ingenious. I seem to remember, when my 750 went in, there was also a bit of tilting required, it didn't just go in on the same vertical plane as the frame. Difficult to be sure that was the case, as it was all a bit frantic!
Not that it defeats the invention, if that is the case, leave some wiggle room to be able to tilt the frame towards / away from the engine, perhaps creating any tilt with some thin wood offcuts slid under one side of the bottom frame rail.
Be interested to hear how it goes. If it works, I'd buy one!
Martin