Hi Gang,
I am part way through a winter project replacing 2 bent tubes from my PX-10 frame, and after measuring the lengths and angles of the (somewhat bent) frame, thought I might approach the list for background info on PX-10 frame angle development. My frame was built in 1970, and it's a big one at 62cm ctc. I've measured - and extrapolated - the dimensions to be 76 degrees seat tube and head tube, with the top tube length 1 cm shorter than the seat tube. These are pretty steep numbers. For the duration of my ownership of the bike - since 2003 - it's been used as a fixed-gear commuter, which may mask the handling somewhat, but it seems to steer just fine.
Cheers,
Larry Strung