The Vintage Gun Grip link for Trojan replacement butt plates may be O.K., but they are a hard plastic. I believe original Parker Trojan butt plates were made from a hard rubber. Galazan lists 2 sizes of hard rubber replacement butt plates for Trojans, 5 1/16" and 5 5/32"--both regularly $48 each on sale for $20 each. Here's a link to the larger size which I believe is the correct size for a 12-ga. gun (not sure if 5 1/16" is correct for a 20 and 16-ga.guns):
http://www.csmcspecials.com/ProductD...PB310&CartID=2