Upper mids bright? Treble bright? Lack of lows can also be perceived as bright.
For upper mids I'd go Nordstrand 60s or SV.
For treble I'd go Duncan Apollos.
The Aguilar DCBJs are the closest passive pickup you'll find that get close to EMGs.
I live a bit further south than you. And I also had a few 90s Stingrays with unstable necks. Not uncommon for that era. Any roasted neck would be fine. Any neck with stabilizing rods will also be fine (Warmoth, USA Fender).
The P pickup is a but further toward the neck than a traditional P bass. Also, the pots might be a different value. The stock pickups in those are ceramic, not alnico. They sound good but not quite vintage P to me.
I love GK. Long time user of their 800 and 700 RBs. Their class D stuff is not in the same league IMO. I've had the MB 200, 500, Fusion, and a combo. All had issues, all were noisy.
This happened to me on ebay last year. The tracking details for the bass showed a weight of 1lb and an origination from China, not USA. That was enough to get my money back pretty fast.