My 2c...
I'd try a little jbass or little wooden knob as others suggested, if you don't like that, then mount a mini switch there (tap / series / parallel on your HB, or something) and drill a new hole. Pickguard can't happen on that clean design and great top, sorry.
As to the pots issue, this is not really a pot value issue, it sounds like. First off, pickups aren't 'designed' to work with certain pot values, it's just that the 250k pots bleed off a bit more treble than 500k pots, hence 'warming up' a single coil, hence that's what they used back in the day. Nothing wrong with SC pups and 500k pots, and anyhow the pot value doesn't make a huge difference. Sounds like your neck pickup is just too bright for your liking - try adding in a .01 cap to the circuit (maybe on that mini switch), or even just lowering the treble side of the coil away from the strings a bit. If that doesn't work I'd just get a new neck pickup that is more your style. Lots of great guitars have SC and HBs together, and pot values are just not an issue.
I would definitely experiment with knobs, mount rings, caps, and pickup height to solve your issues before doing any drilling to that nice body.
I'd try a little jbass or little wooden knob as others suggested, if you don't like that, then mount a mini switch there (tap / series / parallel on your HB, or something) and drill a new hole. Pickguard can't happen on that clean design and great top, sorry.
As to the pots issue, this is not really a pot value issue, it sounds like. First off, pickups aren't 'designed' to work with certain pot values, it's just that the 250k pots bleed off a bit more treble than 500k pots, hence 'warming up' a single coil, hence that's what they used back in the day. Nothing wrong with SC pups and 500k pots, and anyhow the pot value doesn't make a huge difference. Sounds like your neck pickup is just too bright for your liking - try adding in a .01 cap to the circuit (maybe on that mini switch), or even just lowering the treble side of the coil away from the strings a bit. If that doesn't work I'd just get a new neck pickup that is more your style. Lots of great guitars have SC and HBs together, and pot values are just not an issue.
I would definitely experiment with knobs, mount rings, caps, and pickup height to solve your issues before doing any drilling to that nice body.