what is the deal with my 225 /six compression?

Leaks from the spark plug tubes are so common, some wags here term them "drool heads". The seals are cheap and available (rockauto, ...). Later slant heads (1977+?) had a solid spark port. You could change to those someday, but you can't pull your lifters out without removing the heads. Changing the valve cover gasket is easy, especially for your early engine. Some people pull the cover twice a year to adjust valves (a bit anal). Don't over-tighten the bolts and hammer flat bulges from prior owners doing so.

Re what other engines had removable spark plug tubes - the infamous 429 Hemi. Thus you can call your slant a "Hemi 0.75".

Your compression readings are great. I have never measured >145 psi in a slant. The value depends on many things, like the camshaft installed. Besides all cylinders being uniform, another metric is that the pressure reaches the final value in 2-3 compressions. If it takes 7+ pulses to reach the final level, you might have bad valves. It is also easy to get bad readings - if your gage isn't well-sealed, the Shraeder valve at the bottom is not the special light one (white), if the volume of the threaded part isn't proper, ... To insure a good seal, best to remove the spark tubes before screwing in the gage.