Help Identifying Controls: Fender active P/J

Hi Bass Peoples,
New member here, though I've been lurking and gathering knowledge from you fine folks for a while now. Longtime guitarist, recently getting much more serious about the bass, and developing the callouses and stronger forearms to prove it.

I have been fixing up/modding guitars for a while, and I'm in the process of fixing up basses for a friend while I decide on a bass for myself. He scored a mid-90's MIM Active P/J (according to the serial #) for cheap, but this thing needs help.

There are 2 split-shaft knobs. Both pickups are always on, unless I turn the front knob and they both go off. The front knob seems fused or is it only a master volume? No matter which part I turn, top or bottom, the whole thing rotates. I've removed the knobs, and the pot is split, but it turns as one unit. I've used pliers and turned the top shaft while stabilizing the bottom and it's master volume. Ditto when I hold the top and turn the bottom. Is this what it's supposed to be?

Front - volume
Rear - bass / treble boost cut

NECK ISSUES
Seems like the truss rod is busted as the action is high and it's not responding to turns. I replaced the broken nut- it was broken in half, only E & A) I sanded it a down to lower the action a little, but it's still high. It was high before I replaced the nut. Low E measurements:
1st - 1.25
12 - 3
17 - 2.7

Seems high to me - any thoughts here? When I worked on his Carvin SB 5000 that action was low all the way up, like 1.75 at the 12th fret for the low B.
I am considering sanding the nut down a little more and adjusting the saddles to see if that could work. Do you think it'd be better to replace the neck altogether?

Thanks in advance for any help.