#1
I'm strongly considering getting a strat and a P bass (or Fender Jazz?) and sticking em together. I'll just cut off one outer third of each and stick em together. Couple questions:

1) What to do about the arm carve/belly carve? Any ideas how to fill in the carves that'll be in the middle of the doubled up body once everythings glued up?

2) Bass or Guitar on top?
#2
I suppose you could cut out the strat's belly cut area and glue in a flat block of wood.
You could also glue some wood onto the belly cut and then plane it flat against the body.
Or just use a tele body on the bottom half.

The bass neck should be on top. It has a longer neck and it makes it easier to reach the low notes.