You'll want to contact the resident specialist regarding matters like this. He posts under the username Southside Glenn. I don't have time to get into how knowledgeable he is in all things audio, I will say that he is by far the most skilled of all users on this BBS.
BTW, ez, the Leslie idea is an old one. Send the mono signal into the Lez, mic opposite sides of the cab and hard-pan the inputs. It's just a mechanical version of ping-ponging.