I believe the left hammer is a Parker hammer but from an earlier gun or the gun may have lost that hammer and the owner had Parker send him another one. If you have the Parker Story or some other book that shows hammer guns built in different years, you can see how the shape of the hammers evolved. The earlier hammers had a more open internal curve where the later hammers had a more compact curve. The more compact curved hammer had a longer distance from the thumb to the striker to make up for the more compact curve.

JMHO!

Thanks to all that responded.

The owner of this Parker had visions of upgrading his retirement years from living in a trailer court in Wisconsin to the warm and sunny beaches of Kona with its sale. I hope he's not overly disappointed.

Odd in that it is significantly thinner in the other side and what is more often seen.