I simply don't understand the "they said the compression should be around 120 for a 195"....makes no sense to me.
But I will say 120 is LOW compression for that engine and 150 is ACCEPTABLE. Other than that I trust Mike's judgement and knowledge on the matter. He know his sxxt.
I don't, however, think that it would be unusual to find tight valves, across the board, on an engine. Theoretically, that's exactly what you want...everything wearing evenly and at the same rate. If they've never been checked or adjusted, then it IS entirely possible that they are uniformly tight. I don't think that is the cause of your issues in this case but making sure your valves are in adjustment might still increase the engine's compression and, as a result, performance.
The fact that it "picked up good" with 1/4 choke means she's running lean and, again, I agree with Mike that you are probably on the right track. If it's not the filter being somewhat plugged then it's likely to either be a weak fuel pump or some dirty carburetors causing the missing and backfiring.
Good luck and keep us posted on what you find.