gyozadude

If you have a good set of calipers, measure the ID of the seat lug area at different angles. this can tell you if the seat tube near the clamp is ovalized. Some folks have used a large diameter plumb-bob (metal) to insert and tap to get the hole round. Some have inserted a large, flat screwdriver or small pry bar into the rear slot to spread the top of the seat tube at the clamp and this can also bend back out the clamp rings which may no longer be flush. This can be a tricky operation if the metal is already fatigued and cracked. You could ruin a seat lug, so it isn't without risk. When the sides are too narrow and the rear is elongated, I have taken a hammer to the clamp with sacrificial 6mm binder bolt inserted and nutted and used a flat, dull chisel to strike the pin to flatten the rear seat lug area a little to get it back into round with success. But these were often with TIG welded, cheap steel frames with large welded or brazed surface area where clamp rings attach to the seat lug or were cast as part of the lug. And NOT a fancy lugged road frame that takes a Campy style 19 - 22 mm seat post binder bolt. If the frame is really nice, I will prep the area, heat it and bend it, then quench it, and ream it and then repaint it.

Mind you, maybe the specs are wrong. If the measurements on the caliper and consistent and the hole is round and it takes a 26.8 or other seat post and the clamp rims don't seemed overly bent, then go with the smaller seat post.