Very Beautiful, Bruce.
Never say Never, but I would not have expected to see those hammers on a gun lower than Grade 5. The double spur hammer is also present on the New York Salesroom gun you have shown in the Quality C thread. They are very much more elegant than the more commonly seen single spur hammer usually associated with Grade 4.
I believe someone once offered offset firing pins, but not sure. Is that something your friend could consider? Maybe the bushings too.
Also, worn axles seem to be an issue, though that could also be wear in the lock plate.

I know that firing pins ( called plungers by Parker) , both the offset type for lifter actions and the straight type for top actions are made by a PGCA member and we didn't want to interfere with his business.

Your comment about high grade hammers is well taken. Some time ago I posted a photo heavy thread on hammers. I will try to find that and re-post. There were some spectacular examples.

I havent seen a lot of parkers, but of the three hammer guns I have the stirrups in both locks on all three were either well worn and damaged or poorly replaced with something hand made. No idea what others experience is with these small parts.

Check hooks are a good idea. I have broken one. The other parts I seem to have problems with are top lever springs and hammer screws

I have seen those hammers on as low as grade 3 hammer guns. But not many.

It definitely depends on the era of the grade 3 as to the design of the hammers.