to AAPK, Stephen!
I'm not certain this is what you're talking about, but for the knife in my pictures I had it disassembled in an effort to correct a couple of flaws and mod it up a little, but unfortunately I don't have the necessary skills and/or patience to do work like this successfully and it ended-up sitting on my table in pieces.
I had just bought it and wanted my new knife to operate properly, so I sent it to a member here whose handle is "Muskratman" and he is a skilled maker/repairman/seller of many kinds of knives, autos in particular.
When I sent it I kept the original rocker mechanism which included the button arm and cap, and sent one that I had been able to put together from parts I'd bought, similar to what you want to do with a hex head replacement, I think.
Since I knew he was making and installing new covers, I left the cap off loose so he could do the proper measurements for the hole, and when ready he soldered the cap onto the mechanism and reassembled the knife.
I wasn't sure what Mike Sitton knives look like, so I searched and found some examples, which I probably should have done prior to posting this since his knives are not at all like the example in my pictures, although, the principle is the same so perhaps this would work for you too.
Before you dig in too deeply, be aware that autos like Mike makes are likely easier to dis/reassemble than the Italian auto I posted, remember what I said about my lack of skills, so the project might go really well for you, at least let's hope so.
In any event, good luck!
This knife was purchased as an 11" AGA Campolin "Maltese" lockback, and had Brazilian horn covers, a standard SS round button cap, and a safety, the changes I made are the black ebony wood covers, the faux sapphire button cap, and the eliminated safety, and IMHO M-man did a great job!