Just put "Dark Star Pickups" in a search. That'll take you to Fred Hammon of Hammon Engineering...he has retro-engineered pickups (w Rick Turner), which have a sound & depth that emulate Jack's (& Phil's)..as his major influence. (mine as well)
Yeah, that "Crown of Creation" ,et al , timbre is something else to hear. Nothing like it...mindblower...A lot of it is that Alembicized Guild Starfire Bass II.
Its stereo wiring = sound separation of those 2, low-impedance humbuckers, must lead to less interference, clearer sounds....a good notch-filter-type sound. Now that Dark Stars are around, tho, you might get pretty close w many bass rigs. Fred's site gives a great explain here...and, he answered my questions via email. People want to put them on lots of axes.
Jack used an overdriven tube amp known as a Versatone Pan-O-Flex. But, any OD-able bass tube amp, (or, tube effect, maybe) plus the right compression + EQ - obvious on the albums, & in the sound - should get you pretty close.
I put up (in another post) that the actual shape of that (semi-hollow) Guild seems important if you really want to nail that particular tone to the nth degree. Like a violin or a cello - that hollow shape does part of the magic on those Airplane albums. An old principle, but, still relevant as ever....Fred's explanation on his site, Hammon Engineering, covers most of the pickup's role.
I play an Epi, 1999 Jack Casady Sig. Bass, btw, using Alembic strings. This semi-hollow body is the greatest in that way. A real chordal, overtone-laden bass...Come to think of it, Jack used Pyramid Gold flatwounds for those albums/times. Alembics are brighter - Pyramids (haven't been there yet, prob. should get some) have less treble, of course. Good Luck!