It certainly looks like a steel post. I appreciate where you are coming from on the front rim. It almost looks like the sidewall has serrrations but I think that has something to do with the resolution. It appears to have eyelets, an undrilled presta valve hole nad the tire appears to have a tubular lacing cover strip.

Routezab, everything is consistent with a circa 1976 PX10 save for the lack of Reynolds decals (which can become quite fragile) and the aforementioned components. However, it is curious that the fork chevron decal is placed so high as to preclude a Reynolds fork decal. As mentioned there does appear to a ghost outline of a Reynolds decal on the upper down tube, in the vincinity of the shifter tips, however I would be taking my calipers along with me to verify the inner diameter of the seat tube and the diameter of the post, to ensure it is a Reynolds 531DB frame. It's better to be safe than sorry. In that condition I's also be sure to check the stem and post aren't siezed.