""He cant get them to unscrew from the breach."
Ah. OK, sort of lost the bubble.
I don't think I'd need to make a mock up because I've frozen large parts that have been screwed together, or which have large bolts running through them, and have had more than considerable success over the years.
A few years ago my Mother wasn't particularly happy to open her deep freeze and discover the alternator for the garden tractor. The blind bolts holding the casing together simply refused to budge. Three days in the freezer at 20 below, along with lots of Liquid Wrench, resulted in three of the four bolts breaking loose fairly easily, with the fourth requiring only a few taps on the wrench handle with a hammer.
Another freezer success story was this light fixture:
It had hung on the house from 1903 until the 1970s when my Grandfather replaced it with some ugly non-period coach lantern. Mom found it in the basement, quite rusted and in need of rewiring.
To do so I needed to get it fully apart, which included the arm, held in place by two long carriage bolts, and four screws holding the backing plate in place. That one was a real challenge due to it being very difficult to get penetrating oil to where it would do any good, but after several days in the freezer, all of the screws and the two bolts released easily.
A little rehab, rewiring, some paint, and the proper light now hangs back where it should.
The only real failure I've ever had with cold sinking was on an engine block to an old John Deere tractor. But, to be fair, heat failed on that one, too, and we had to drill out 7 of the 12 bolts and chase the holes.