Greetings Trot,
I have a Griffith Hawken lock and matching 1" breech plug and hook tang. The hook-on breech and tang are NOT slant breech design, but straight. This straight design was more common to J&S Hawken rifles. The slant breech design seems to have been used almost exclusively on S. Hawken's and J.P. Gemmer's Hawken rifles. Now I just know that somebody out there is going to post an example of an exception to what I just wrote. OK, my shoulders are strong: I can handle it.
Back to the Griffith lock. I purchased mine in 1985 and it is exceptionally high quality The main spring was very, very strong and had to be reground to a lighter fall.
As I understand the story, this lock was patterned after an original by the 2 Griffith brothers and produced in THE GRIFFITH MACHINE AND TOOL COMPANY. Several years or more back, the company was sold, and the lock produced under a different name that I do not recall.
Hope this will help you.
Best regards John L. Hinnant