Here is some information direct from the gentleman who produces the CNC programming for all of the bodies.
"Same body, just different routes. The 51 has a route that the metal plate covers. Also, the split coil route is cut to the shape of the pickup vs. rectangular. If you are interested in a 51, I have an extra coming up with a buckeye top and a cool roasted neck with roasted birdseye. Short wait!
A 51P Technically has a slab body with no contours. A 51M is the same, but WITH contours. Same as the 4464"
There seems to be a very unique 51 that is coming up.
If you're interested in it please PM me and I will give you the contact information for Steve at Lakland directly.
I might be interested but I don't have the spare money right now
Maybe you can benefit
Good luck.