When I first spruced-up my Nat'l Aristocrat, I thought that the shortcomings involved with the original pickups might be overlooked (low output, obnoxious rattling issues, bridge top moving around on me), but after playing it for a week I decided they were definitely not "doing it" for me, so I ordered the necessary parts and went-ahead with my original plan when I first saw the guitar (installing a new electric pickup and a K&K acoustic pickup -- individually available on a stereo jack).
I've always wanted to install some sort of Jazzmaster pickup on, well, a jazz guitar -- so I grabbed a Seymour Duncan "hot" JM neck pickup and installed that in a surface-mount fashion (I had to shorten the cover a bit) in place of the original neck pickup. I am well-pleased with the result.
I have to admit that my favorite pickups are P90s... followed quickly after by P13s (the P90 predecessor)... and after that the DeArmond Dynasonic pickups one finds on 50s Gretsch products. The "hot" JM pickup is built mostly like a regular Jazzmaster pickup except the coil is brought-in a bit closer to the poles and wound hotter. This fortifies the bass and lower-mids and gives a bit more growl to the otherwise-normal bright, sweet, and clear tone of the pickup type. It's exactly the sound I need for this application -- like a mix of those Dynasonics, a P90, and the clarity of a Fender design. I like.
Having the big Jazzmaster cover helps in disguising the pickup's age, too, as at-a-glance it looks a bit like a P90 at first.
I replaced the ailing in-bridge "acoustic" pickup of experimental design with a new rosewood "saddle." Note how far the adjusters are from one another to accommodate the old unit! Under the "wings" of this bridge are two K&K Big Twin pickup sensors glued-up under the top.
Two volume controls -- one for the magnetic pickup and one for the acoustic. This way I can feed two signals to the board (or to two amps... or whatever) and turn one on/off by just killing the volume. Because the top is such thick ply on these old Gibson-made ES-300 bodies, the tone of the K&K is a little peaky in the upper mids, but dialing that range out yields a tone a bit like a cross between a clunky J-45 and an old archtop. It'll work!