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That's a tough one. I've never played a true P90-sized humbucker, but it seems like every winder and their brother offers a humbucker-sized P90. Haeussel is the only one I know of that's got something like you're after. Another option would be to have one custom made, which is possible with a little elbow grease. Mini-buckers are sort of like this, but it'd be interesting if the coils were taller to accomodate more wire.
You may not need to rout your vintage LPs to use the Kinman. If your stock rout is at least half an inch deep, you may be able to bolt it right to the wood. I did that on my PRS SE One and the coupling is phenomenal.