273 Commando Rebuild Or Not?

The head gasket is not you problem on the low side. Check your head castings. If you run the engine as is and start using good oil and a good filter, the compression may come up to match the other side. Commando head gaskets are special .020 thick head gaskets. The bore of the Commando head gasket is not round, you will not find another set like, or as good. 2 and 4 barrel springs are different, but still lacking in spring rate. 340 valve springs are great on any HP small block and were readily available at a reasonable price. You can also run aftermarket copies, see post #13. There is no down side to running 340 valve springs, and if you are replacing the valve seals it is easy to swap the old springs out for fresh better springs.
The possible downside to running heavier valve springs is the extra wear on the cam and lifters. If it's just going to be a cruiser and not going to be revved way up, why do it? No upside IMO. The existing cam and lifters are used to those springs.