This is the bass I'm looking to modify:

So, what about this idea? I'm thinking that I could have another MM installed in place of the current neck pup (with the rear coil at the 36th fret location), and move that neck pup up to the 24th fret location. I have a switch installed right now that allows me to choose either or both coils in the stock MM - I could do the same for the new MM so that I have the rear coil (at the 36th) and the new neck pup (at the 24th). I know these wouldn't be exactly (or even nearly) like actual Ric pickups but they would be single coils in the correct spot.
This would be a monster of a bass!! I could use either MM or both, get J tones from soloed MM coils, or get Ric like tones from the rear middle MM coil and the neck pup.
The only issue I can think of is that MM pups are not quite as wide as a J neck pup. A J neck is 3.6" across and the body of an MM is 3.5, but this is a minimal issue. The only other concern would be the MM screw bump(?) on the control plate side bumping against the plate, but I don't think that's going to happen.
I would leave the electronics passive. Each pup would have their own push/push pot which would also be tone pot. I'd have to put the front/both/rear coil switch for the middle MM in the pickguard using a black toggle switch (so it didn't stand out too much).
So, what do you think?