There is a small dent on the seat tube, about 2.5" from the top. That must be what I'm hitting. There does seem to be a fair amount of oxidation on the inside of the frame, at least I see an orange hue when I check with a flashlight.
I would not know how to go about filing, sanding or reaming the inside of a seat tube, but I am taking it to one of Boston's best frame-builder's, Peter Mooney, and he'll know what to do.
If fate has it that this seat tube is 26.2 (Sheldon Brown said some straight guage 531 was 26.2 i.d.), then I'll get one that size and sell the Simplex.
I really didn't think the small dent would affect the inside of the tube, but I expected a lot of surprises when I began this project.
Miele, this frame has no bottle mounts.
Thanks for the suggestions.