I have gotten a bunch of work done on the T16s, and photographed them!
Here's the back plates cut to size, and the backs of the T16s edged to put them in place. I have seen restored T16s without the back plate, but I think it's an omission rather than something actually done at the time.
After the lower plates were glued in, I then drilled out a slot for the magnets. These are my big (for models) 1/8th inch cylinders. They're good and strong, and actually let me get away with using just paperclip to hold the guns in place! This is much easier than trying to drill out a hole for a magnet on a pair of recoil struts.
Speaking of the guns:
Here's what they look like attached to the base, but separate from the T16s. The back end of the T16 would be more detailed if they were ever on the field without their guns. The paperclip is buried between the rails and up against the scoops, which are just thin bits of leftover plasticard. You can also see in this the travel bag that went over the muzzle. The wheels in this picture are the earlier ones I cut; as soon as I saw the way they looked, I switched to cutting them much closer together, so the notches look more like a field tyre than an off-road jeep.
Here's what the gun looks like attached to the T16. You can see that with it attached, it'd be nearly impossible to tell if there was indeed a trailer hitch or not, and in fact adding one would probably make the magnets not stick properly. As it is, lightly dragging the T16 forward brings the gun along with, which is exactly the strength I want: Strong enough to stay together, loose enough to separate for ease of travel and tight corners.
On this one you can see the tighter cut wheels (in the back left, for example) and all 6 in place! Behind them are models from the Open Fire set, some Oiran, and some High Elves. (because one project at a time is for the weak!) Now I just need to add camo netting to the guns for them to be done, and for the carriers: it's rifles; clutter stowage (including ammo); crew; small bits of oddity; painting; more oddity (I'm hoping to do pinup pics in one or two) and done! (Well, then I paint the actual platoon of 6pdrs...)