If it looks like these amps, you have the timeline right on. 1965-67. These were the last series of amps built in Kalamazoo MI. My Minuteman is second from the top, in the middle.
I have had one for about fifteen years. It took a while to find a nice one. That being said, there is not much call for them. You might check with Chicago Music Exchange to see if they are interested. It is a beast! They are rare and were very expensive when they hit the market in 1970. Lester himself used the preamp with a smaller powered speaker right to his death as far as I can tell.
Lesters amp
The guy I play guitar with bought one of these when they came out........
Vintage Gibson Les Paul Studio Baritone Electric Guitar Dealer Sheet/Print Ad | eBay
He has the redish orange one. Other than having to compensate for the odd tuning, it's fun.
You really don't see many of these pop up used...........
These flat wound chrome bass strings came new on one of my Gibson basses. I have bought them for three others. They kind of tame some of the string noise.
I’ve had three LP’s with cracks in two or three of the knobs on each guitar. I think that they were likely shipped that way when new. I bought a set of after market knobs off of eBay for each LP & they were a perfect match. Non of the after market knobs cracked when installed.
Going back 50 years, my ‘67 ES-335 with a Bigsby came with a thicker Lifton case. I thought the guitar flopped around too much & found a thinner 70’s era case, it fit perfectly. Gibson must have allowed extra room for the Bigsby on the OHSC.
I have an ES Les Paul guitar & Bass, they both have the “F” Hole TRC. One is a 2015 & the other a 2016. A friend bought a 2015 & it has a plain TRC. Sounds like random part supply issue……..