I checked out the pictures. The Bart J looks like it was a wonderful fit and the P doesn't look like it's a horrible fit. It looks really nice on the black and the gap is hardly noticable. Ive seen some pickups that look like it would be real easy to swap out the covers of the P pickups as long as the base of the pup fits in the cover. I think the J pups are the best candidate for swapping out as the P pup sounds pretty good to my ears.
I guess the weight of the tuners make it so about the only good swap would be for an expensive set of super light tuners. I was going to swap mine too if I ever find a good replacement that would offer equal or better performance and equal or less weight. Do you know the size of the posts?
GassieBall- Here's a link to page 17 of the Short-Scale Club where Mongo talks about his stealthing of his Mikro.
http://www.talkbass.com/forum/showthread.php?p=7525470
(sorry about the bad info, I thought it was in the Ibanez Thread.)
What color is your new bass? It looks to me like even if you want to replace both pups in your Mikro, the fit is nice and even if they are smaller, the gap isn't noticable.
We need pics!!!