Dude I was wrong about one thing. Green is the lead wire and the bare and the black should be connected together, but it dosen't really matter, should be the same result.
Well, an original GP-1000 won't give you a bodom sound, and they go for more than they are worth because it got the reputation that it is one of the best preamps for metal out there when it really isn't (original that is).
Just keep your EMG for now, it's a better choice until you have something to connect the J-50BC to. Because without a boost and some EQing it would sound sterile and sharp, without any real definition. It really is just a clone of the old PAF humbuckers. I bet you could take any PAF clone like the Dimarzio PAF Pro or the Seymour Duncan JB SH-1 and get almost the same sound as the J-50BC.