Scott:
Remember the commander's mounting on that Panther turret cupola? That set-up, just like the set-up I put on my E-10, serves as a somewhat crude night-vision gun-sight for the main gun. And that function really does not differ between "traditional turret" and casemented main-guns, such as you are working on, or my E-10!
What you need to know about this is how deflection in the IR unit - traversing right or left of "straight-ahead" - translates to the actual gun-sight, gunner's position, and direction that the gun actually points in.
In the original case, this data - the "compass-bearing" of the IR unit, as a deviation from the compass-bearing of the gun-sight and gun-tube - was likely relayed by a mechanical "metal tape" linkage, as was the elevation angle. Much like older-fashioned big guns on battleships, where the gun-sight was distant from the gun.
So... that commander's unit had a very limited left-right traverse - if any at all - relative to the main axis of the gun. Unless that IR unit could decouple from its data-transfer mechanical linkage, it's traverse would logically be limited pretty much to the available traverse of the gun. On a casement gun (E-10 or E-100 jagdpanzer?), the gun would be able to traverse a few degrees left and right of center, and that IR set would likewise probably traverse a few degrees L and R. This would not make using it for an MG mount very practical...
For that turret mount, it may well have been pretty much fixed in parallel to its main gun - and rigged to communicate elevation angle info only (as the gun did not traverse within its turret). Seeing as the commander could either direct the crew to traverse the turret, or could do that himself, in order to acquire the target, there would be little benefit in having this mount traverse.
On the other hand, for that IR-MG mount to be very useful, the MG gunner would need to be able to rapidly traverse his IR set and its weapon, and over substantially greater amount of arch. This would mean that it probably could not be mechanically linked to the main-gun sight or tube... as that MG was likely to get pointed quite elsewhere than the big gun. So, I would guess that you can have it serve one function, or the other, but not plausibly both!
In my E-10 mount, I accepted that the main gun might traverse ca 7 - 15 degrees L or R of center, and concocted my IR mount to accordingly swing that amount L or R of center, along with the historically-established metal tape elevation relay device. IF I was doing an E-100 I would probably go this route with that beast, too.
I had (briefly - as I actually only had the one IR set-up to work with) considered whether I could maybe mound an IR tube on that MG mount (perhaps as an under-barrel sight). As the real "rundumfeuer" MG mount had a periscope-sight under that MG, so I figured I might mount that bildhandler to "feed" that periscope. But it looked like it was going to be pretty bulky and so I let it go. Note: that bildhandler is an in-line photo-multiplier device which projects a tiny image on a view-screen at the back of the tube. The operator thus is looking "through" the bildhandler just as if it were a telescope. There was no remote, wire-connected view-screen, so this geometry would dictate how you can actually place your IR device. So, for the rundumfeuer mount, it would have to sit in front of the periscope lens.
Cheers!
Bob