Mike Lull and Jason Lollar make 60s T-Bird pickups based on their analyses of originals, and they're humbuckers. Bill Lawrence told me they were blade magnet humbuckers. Lindy Fralin and Seymour Duncan think they are too. So I think we can be sure that some of them are humbuckers. I've never heard of anyone mentioning single coil 60hz hum on a 60s T-Bird.
OTOH if you can find an example of a single coil 60s T-Bird, it would not amaze me. You never know with Gibson.