As I begin planning a custom strat, I know that what I want is two Duncan SHR-1 pickups, and one vintage Gibson humbucker. I would be grateful for any advice on the electronics, placement, tonality, and so forth involved.

Thanks,
D

Welcome.

Your questions are somewhat bewildering. You state you know what you want for this build, yet you want to know everything about everything which you have already chosen and how to put it all together. This leads us to perceive that you haven't considered, researched or planned anything beyond a basic, cosmetic stage. If this perception is correct, you'd have to first go to the Duncan site and start researching the attributes of the SHR-1s and then research the attributes of whatever this aforementioned and unnamed "vintage Gibson humbucker" may be and then how the three pickups will interact tonally with each other for starters.

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You dig?

Im going to assume you mean a PAF when you say Vintage Gibson, so from there; what are you playing? If you want a fat bluesy sound, put the humbucker at the neck, if you want it for solo's, put it in the bridge. If i was putting a humbucker in a strat, I'd put it in the bridge position, an Tele; the neck. The pole pieces probably wont line up if you dont buy it F spaced, but this doesnt affect it nearly as much as people think.