Thanks Enfield:

C42534 should be from 1957, and should be from Greener. Look for the date code (I'm assuming both of these were proved in Brum) to check that. This mark will appear as a pair of crossed swords, with letters in the 9 and 3 o'clock angles, and a numeral at 6. For 1957, the letters are HB. If not, what are they? The letters are quite small and may require good light and magnification to make out.

For G75981, we'll have to rely on the date code. It's a late gun, built during the Webley period, I'm thinking maybe '72 to '74 as a wild guess. There are no annual serial number details available for this period. The date code letters for '72, '73, and '74 are XB, YB, and ZB. Which is it?

Hope this helps you.