J pickup that would pair well with a G&L SB2 pup in a P/J?

I think the DiMarzio Model J is probably a good match, because it has high output to stand up to the MFD split-coil, which IMO has some similarities to the DiMarzio Model P. (I have an SB-2 and used a Model P for awhile in a Fender.) You could consider a Barden as well. I've used those in a Fender Jazz V, and IMO they're like two thirds J pickup mixed with one third MFD humbucker, so maybe they'd go well with the MFD split-coil, but they are expensive.