I surprised at the double slug nature of those pickups. I recall buying some double slug humbucker pickups back in 2004/2005 and everyone thought they were junk because they had no screws.
Now I have recently seen Gibson double slugs on a colleague's workbench.
The H-series Andersons actually are said to use vertical magnets, a very different design from regular humbuckers. I suspect those slugs could be rod mags like the ones typically found in singlecoil pickups. Thia yields better split tone because the magnetic field is stronger and concentrated in a smaller area.
Back in the 1980s, the original PRS humbuckers used rod mags in their slug coils along with a conventional bar magnet underneath. I credit that feature for part of the extraordinary clarity which has made them legendary.
The double slug Gibson hums are a conventional design. Some were made like that.
What about a hot humbucker, say around 9.5k in the neck??? That may have more output even when split???
Yes, the hotter the pickup, the stronger the output when split. I've seen even high output humbuckers like the Super Distortion or even the JB used in neck position. Of course, there's some trade-off in clarity when running full series, but the split tones are indeed stronger.
Some medium output humbuckers normally used at the bridge can work very well indeed at the neck. Perhaps a Jazz Bridge instead of a Jazz neck? A little more mids but perfectly well-suited to neck position, and better when split than the neck model. (The regular Jazz Neck splits pretty well too, but wouldn't be able to stand up to a JB.)
One slightly hotter example is the Duncan Screamin' Demon at just under 10K; it's got a nice PAF-ish voice yet uses a modern wind that's relatively tight & crisp sounding. Great pickup for neck position - especially in a maple-neck Fender-scale guitar - and it splits well.
Another good choice might be the 59/Custom Hybrid; they run around 11.5K but have quite a bright clear character thanks to the extreme difference between their coils. When split to the more powerful Custom coil they have decent output and good tone.
The 12K Duncan Distortion neck model has a ceramic mag and is hot & bright; it splits very well indeed. I've used this pickup at the bridge (it was originally designed for bridge - it used to be called the SH-7 Seymourizer). Holds up very well under lots of gain. A bit of ceramic stiffness to its feel but IMO that's less critical in neck position.
There are also some humbuckers made up of two actual singlecoil pickups. Unfortunately their series tone tends not to be as smooth as a regular humbucker. Not sure they'd do too well at the neck.
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Are you totally sold on split wiring? Perhaps choosing a very clean humbucker could render that unnecessary. Something like a PowerTron or a TV Jones or a Lollar El Rayo might suit you. Or even a hum-sized P90 if you were willing to do without hum rejection. I love P90 neck tone.
