Please understand this is just my opinion.The best that things ever going to sound in a Alder body is with it hooked up to a 250k pot? The lower resistance pot helps make them bearable but I still find them very lose & sloppy sounding. 500k pots will tighten it up some but the pickup will basically become useless for anything that doesn't have a S*** ton of gain on top of it! They become shrill & make it sound piercing in Alder or other similar tone woods?
I'm telling you, it can't really be improved? It can be tweaked a little bit but when you "tweak" JB's it's always a compromise someplace, if whatever you do improves one area it will undoubtedly cause adverse effects to another. Bottom line is it works well in some guitars and for some people but chances are if you had problems with the pickup in a Poplar guitar you will have the same issues with it in Alder?
Oh, you may or may not like the maple neck with the JB, they say it works better with Rosewood but I actually liked it better in a Strat with a maple neck? I guess it's a matter of preference & you're going to find out soon enough, right???