I just posted this elsewhere, but thought someone here might like to know:
Interesting you should ask. I have F (1949) and H (1951) pre-fixes, and I have two "Williams Auxiliary Hammer Extension", as they're labled on the instruction sheet. They were not on the Willams website when I looked, but I found one on eBay. Quote:
AHE-W for Winchester 95,94,64,55,etc
AHE-IJ for Iver Johnson, Stevens and other singles (.335x205)
AHE-HRT for Harrington and Richardson Topper
AHE-M39 for 39 and 336 Marlin. Also for Savage 24, Due to the fact that Savage 24's have had three or four different designs of hammer widths, we have used the 39 Hammer Extension for the various models. Some of these hammers have to be dressed down in width.
I tried Uncle Mikes, and it wouldn't work on those older rifles. I found one marked "JM" at a gunshow loose on a guys table, it didn't fit the older Ballard rifled guns, but fit on a 1980's era 1894 Marlin.