hello johnzimbo....you didn't mention where you are coming FROM to the William/GC train trip and where you'll be going back TO...however, I have some suggestions. I lived approx 40 years in the Verde Valley (the area comprising Sedona, Camp Verde, Cottonwood, Clarkdale, Cornville, Jerome) area before I met DonDiego.
IF you are doing a visit FROM Vegas, I would do the Williams/GC train (which I've done twice...it's fun but hokey so take it in stride and of course, the payoff is the Grand Canyon which is overwhelmingly beautiful) as planned. Then drive to Flagstaff, down the switchbacks to Sedona (on 89A, NOT the freeway 89). The top highlights of Sedona are the stunning red rock formations, the famous church Frank Lloyd Wright created (Chapel of the Holy Cross) and the famous "Slide Rock" in Oak Creek.
However, since it is winter, you won't be doing the swim down the Slide Rock and it's not really much to look out without the swimming part (although it has been used/seen in TONS of westerns and other movies). The best bet would be taking a Pink Jeep tour (there are 2 or 3 companies that do jeep tours, Pink Jeep is the only one I remember). I've never taken the jeep tour, but would imagine it would also visit the Chapel. (I personally wouldn't plan any hikes, either, for such a short stay. You don't need to go far at all to see all the beautiful things to see and winter is like winter everywhere, not as pretty as spring/summer/fall)
Chapel in Sedona
After the Sedona visit, I would drive west (on 89A NOT 89) through Cottonwood and go visit Tuzigoot near lower Clarkdale (as already mentioned here). The museum is not that important so it's ok if it is closed. These are small but fairly intact complete set of Indian ruins on a hill. It is really a neat place to visit for an hour or less.
After a quick visit there, I would drive up through Clarkdale to Jerome just a few miles away. Jerome is a 'ghost mining town' with a thriving population. It is definitely worth a visit. You might see the Sliding Jail, walk the main part of town (2 short blocks), buy some copper (which is what was mined here), eat lunch at the Haunted Hamburger. (When you enter Jerome, at one of the MANY hairpin curves, you may see a 3-story brick building now designated as an Arts Center....this was my high school decades ago!!!)
At this point, if you are driving back to Vegas, I would continue up 89A to Prescott, have a drink on Whiskey Row (where Doc Holiday and Wyatt Earp also had drinks...specifically at the Palace Saloon) and continue north back to I-40 and back to Vegas.
Personally, I don't think Montezuma is a big deal to visit. When I was a kid you could actually go up and into the ruins, but now they are blocked off so, in my mind, it is not worth the 30-mile detour to it.
From Williams, if you didn't take a jeep tour, and just drove around yourself, you could actually do this entire loop in one day and spend the night in Prescott for your return trip back. (This is assuming you plan everything out before you go to get the best route) Just google any of the items mentioned and you'll find tons of info. Just fyi, from Flagstaff, through Sedona, through Jerome up to Prescott is like a 90 mile loop...not long.
Oh...btw...to keep your visit happy, I recommend you (and your party) take a dramamine (or similar) before you go. The switchback roads down into Sedona and up through Jerome can play havoc on one's tummy...and why take the chance...