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Specialized's official headset for it is the Mindset, but I think certain FSA bearings will drop in, mine has an FSA top cap and cartridge bearings, certainly. As for clearance, I can measure the frame later, but I only personally have 22/23c tubs to test fit, aside from my gf's 32c touring wheelset. Might be able to borrow a friend's Ksyrium's with 28c Paselas. I've also got an aftermarket LOOK HSC fork, not the original. Maybe @Thrasher can help you out there.
Just be wary of corrosion if you use it over winter, it's very thin tubing
That's me