Joe nailed it!
I found out about this the hard way. My hodgepodge rifle started out as a Deer Creek (CVA) in .45 caliber and a 15/16" barrel. I compared its weight to a .50 CVA Mountain Rifle and it was about (IIRC) a pound and a quarter heavier. I then thought that if 1/32" was taken off each flat it would be about as heavy as the .50. Ed Rayle did that for me at a decent price and I ended up with a barrel 7/8" across the flats, and lighter than the Mountain Rifle.
All was well until I had run 100 or so shots through her when I noticed a ring forming around the touch hole liner. Somehow the milling process had loosened it, or something. Anyway, I now had fire coming out around the liner - bad news!
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Captchee was so kind as to see what he could do with it, which was nothing, really. He then got a Colerain barrel of the same dimensions, installed a regular flat breech plug and set it up with the under rib, etc. which is on it now, and I gave him the old barrel to use as he wants.
In retrospect, I could have had him cut off the breech end and re-breech it, move the underlugs forward the same distance and shorten the rib. This would have saved the price of a new barrel but I thought of that much later, after the fact.
So Rob, you could still get the kit if it's cheap enough and just modify the barrel with a flat faced breech plug, as long as it is short enough to allow you to install a regular touch hole. Just a thought.
~Kees~