I'm not certain but the push-in breechplug may have been used on the old H&R .45 cal Huntsman also... the old Huntsmans weren't all .58's. These plugs usually came with a nipple for #11 primers, but I recall a hunter I met in the woods many years ago who was carrying a Huntsman 12 ga. muzzleloading shotgun which had 209 ignition in it's push-in breechplug.
Hubbard's has a # 209 holder which threads right in and correctly 'headspaces', so to speak. I have one in my .58 which works perfectly, the fat, large diameter firing pin causing no difficulties. Hubbard's also offers their own replacement push-in breechplugs for the old Huntsman. Here's their site:
http://www.hubbardsoutdoorproducts.com/ Another choice is the Flamethrower style in-line nipple made for either #11's or 'TopHat' musket primers. I have one of these musket nipples which also functions flawlessly in my old .58. Check this site:
http://www.gunaccessories.com/ThompsonCenter/ReplacementNipples.asp I'm unclear if you meant to ask if these breechplugs are in any way applicable or compatible with TODAY's Huntsman... if that's the question, the answer is definitely NO.
Steve