I'm in the middle of nowhere and don't own a car. Sometimes I can't buy milk because the only store here that carries it is sold out. Forget about a bike shop in a county of 2,400 people unfortunately.

I did just order a caliper from Amazon. In the mean time, tightening a clamp so the seatpost barely slips thru and then measuring the gap I get about 31/32" (24-25mm) so, bigger than my previous measurement though we were expecting smaller.

The hole in the frame is easier to measure and I'm more confident it's an exact 25.4 inch per my ruler. There's some paint overspray inside the hole so I'm betting it hasn't been reamed.

As juvela said, this isn't watch repair, and the Wald #905 probably would bend to fit. It is a little unsettling that these dimensions don't match up perfectly though, and Amazon doesn't pay return shipping where I live (unless you claim the item was defective) so it takes a bit more confidence to place an order.

(Walmart pays return shipping, refunds my purchase and then never picks up the item! Wth?)

The #905 is $8 so it's in my cart along with some seatposts and I'll sort it out and order soon. I'm currently hesitating to consider a seatpost shock absorber.

thanks for your advice everyone