I recall never measuring more than 140 psi in my 225, even w/ a new rebuilt short block. Before ripping it open, try a few sanity checks. Turn it over by hand with a socket wrench. If you can feel each cylinder like a firm spring, your engine is sound, so try another compression gage. It may not be sealing fully. On a slant, you probably should remove the spark plug tubes first to insure a good seal on the spark ports. You likely need new rubber seals on those anyway. Did somebody put a regular Shraeder valve in the end of your gage fitting? Those will give grossly wrong readings. Maybe the gage's rubber hose has cracks.
I suggest that because I think that with the readings you post the car would either not run or would pour out blue smoke. Of course it could be the valves. If it runs and you have a fairly steady reading on a vacuum gage, then bad valves in that many cylinders is hard to imagine. However, you do say you get some smoke.
I think you can re-ring in the car. I did that in my V-8 C-body with a similar K-frame. I think it is much easier than pulling the engine, but others disagree. You can hone the cylinders with an electric drill and a ~$10 stone tool. Just clean very well with soap and water. You also need a ring compressor (<$10 Harbor Freight). A ring expander pliers is nice, but not essential. Soak the pistons in gasoline or similar to clean well before the new rings. Also replace the rod bearings and maybe the main bearings (can do w/ crank in by pushing the shell around, plus the rear seal. And clean, clean, clean.