I bought a 78 LP Standard that had a JB in the bridge and a PAF in the neck. Never liked the combo, yet each had it's advantages. But... the JB requires a whole EQ/distortion path of it's own when it's in the bridge, cause its' so thin and bright. So I put a Pearly Gates in there and it's the best for the ABB style sound I want.
What I did next with the JB is my answer to the general "How to place a JB" question. I have a home made, 3HB strat and I pub the JB in the middle, in that position, it gets a lot more of the meat of the string, and it plays really well with the SH1 in the bridge, and the Schaller in the neck. With a 5-way switch I get some really cool tones. So that's my solution for the JB, it keeps it's tight high end and gets a little more meat on the bone this way.