The humbuckers that split best have very asymmetric coils, which aren't an especially vintage trait. You might check out Lindy Fralin's Unbuckers, which I've heard good things about, but have never heard. You might also look for an aftermarket pickups/wiring harness from an SE Paul's Guitar. (These sound divine split, with almost no volume drop, and they're still in the vintage range as humbuckers. I just find the series sound congested.)
My humbucker that splits best is a Seymour Duncan 59/Custom Hybrid bridge pup, which is 7K + 4K in series, and sounds like a real single-coil pup when split to the 7K coil. But the 11K series combination is hotter and angrier than vintage.
FWIW, I originally wanted to replace the 85/15 S neck pup that came with my now-favorite PRS guitar. The lack of articulation sounded non-PRS. Then I took it to a rehearsal, and heard how nicely its soft attack sat in a mix with other instruments. Ever since, I've loved it and its bridge counterpart.