It looks early 1970s, but the serial number suggests 1977 which is a better fit with the Cyclone rear derailleur that was first introduced in 1975. If we assume it's the front derailleur that is original, Shimano 600 was introduced in 1976, so 1977 is still a good bet.

The tubeset is almost certainly a butted, CrMo set as stated by Cyclotoine. It's almost certainly Tange or Ishiwata. The best indicator is probably the seat post diameter, which should be marked. Most Tange, CrMo butted tubesets use a 26.8mm seat post. Ishiwata varies a bit more, but if it's 26.8mm or larger, it's good tubing.

A lot of cyclists feel that the Japanese frames from the boom era feel "dead", even on the high end models. Based my experience, I'd have to agree. However, I'm not entirely convinced that this is due soley to the tubing. Many of the Japanese frames from that era have relatively relaxed geometries compared to their European counterparts. This appears the be the case with your Pro, which seems to have realxed angles and long chainstays for a bicycle whose moniker suggests a competition model. Regardless, a very nice acqusition. Congratulations.