Response to Hijacking:
Prying and squeezing a seat lug to make it round amounts to cold-setting. Applied judiciously, no damage. But if it's overdone, it can damage the lug. If the setting seems to take less effort (less overbend) as you continue to try to make it round, the lug/tube metal is seriously weakening at the locations with the thinnest cross-section.
I think the thing to do is to get a post in there that you think might work and torque it to near-spec. If the slot in the seat tube is narrowing, go to the next larger post. Clean the inside of the seat tube and lube it to insert/manipulate the post in the tube. Having the saddle attached to the seat post is a great help with leverage.
With this the lug may become more round, but at least the stresses are in accord with the shape of the metal.
Don't go any bigger than what fits with the slot edges parallel what near-tight. The bolt holes on both sides need to remain parallel and co-axial. Otherwise dirt in the threads will seize the bolt and you'll have bolt breakage, once a year or so.