Hello Rick,
If you go back to a thread in this section titled "Thumb Safety Lever Types" on 11-17-03, you will see the various types.
I will let others contribute to time frame and serial nubmers for the cut-overs...as I am on the road.
Regards,
Pete... <img border="0" alt="[typing]" title="" src="graemlins/yltype.gif" />