W2..
I've been on the same JE/Leeds/Tommy quest for a while..since 1972. I have a set of pu's in my alder body/maple neck P bass made by Bill Bartolini before he started "Bartolini"..they are called "Hi A" . According to Bill, they were made as a higher output version of "classic" P bass pu's..based on pre cbs pu's. That of course may or may NOT be what JE was using, as '66 was transitional, and the pu's might have been..who knows? (sorry) I have found that with fresh roto swing 66 ers, and my Hiwatt dr 200..it gets close to Leeds..but only at a certain volume..the push from the 'watt interacts with the bass, making it sound very different at different volumes. I also prefer the sound of el 34's though, and have been looking for a suitable 100 or sound city..or orange lately. The bass is light for an alder body, at least in comparison to the 100+ I've tried over the last 35 years.
I haven't tried the SD "antiquity" , though lots of wags (not here btw) think they are the schnitz for this sound.
An interesting thing about those slab body P's JE played..3 controls..so maybe an early preamp? I used to play with several of the Vox range..treble boosters, etc.and sometimes the right combination of that and the front end of a hiwatt would be very JE like. As was playing through the front end of a vox SS amp, driving a small el 84 tubed power amp. Lots of strange Bill Wyman tones from that as well.
I have been following your posts re the slab body..and noticed that Fender has made a slab body p, albeit with a jazz pu added..to it's line of "artist" basses, the Frank Bello model. Not being from NYC, I have no idea who this might be, but the bass, a Japanese (I think) p ..looks like it could be a mule for a project. It's certainly cheap enough.
Somewhere in the UK there's a JE slab with a preamp..or 2.
en avant
jp