UPDATE: Well, I took the trigger group out as suggested. I did this once before on an older Model 12 and slightly chipped the buttstock where the "tang" was inlet into the stock (tight fit), so this time I loosened the buttstock slightly - first. After I got the trigger group out, I took off the lifter. But then my disassembly guide said to stop there and to leave further disassembly to a qualified gunsmith. But I could tell at that point that both slide lock springs were there and looked OK. I could also tell that a good internal cleaning was needed. So I basically punted and sent the gun off to Simmons this afternoon for a good overhaul. I also asked them to add 1/2" of spacers under the buttpad to get me to 14".
My wife and I moved into a patio home five years ago - no basement. So I really don't have a good place to do work like this. In the summer we leave one car out in the driveway - that gives me space in the garage for reloading and other projects, but both cars are inside in this weather, leaving me more bored than usual. As a result, by the time spring (and my vaccinations) gets here), I'll have a few more trap guns than I really need. Got to do something during lockdown