I would be very careful to use a reamer on a seat tube that has had the binder slot already cut (as opposed to during frame building reaming before the slot is cut) especially with an adjustable one that has straight blades. The blades can very easily catch on the slot and either cut poorly or break.

I don't have access to Trek's dealer site which has a lot of prior years specs, like the OEM post diameter. Any Trek shop can sign on and search to see if the records go that far back. Of course the expectation will be that you buy something from that shop.

The usual way to deal with this situation is to try to open up the binder area before any material removal. Better shops often have a range of different sized posts to both be used as prying devices as well as gages for tube ID. It's not hard to use a slightly undersized shaft and wallow out a squeezed in binder area. Only after getting REAL close to the OEM post size of fit would I consider honing or reaming. And only then to take off the few "high" points. If I were to ream I would bevel, relieve the slot's inside edges so that a reamer blade wouldn't catch so easily. Andy