Adding Gauges/Avionics: How do Masks Work? Are they a part of the MDL or bitmap?

After doing some forum surfing, I know that the Cessna 172N has 3D knobs, and that makes tearing out and replacing the radio stack problematic. This is not a major problem, since I actually like the Cessna NAV/COMs, ADF, and Garmin transponder. It's all appropriate for this particular A/C (though I am looking for black versions to complement Bill's panel repaint... I know that black models were manufactured IRL). I don't want to shove in a GPS, autopilot, or anything crazy like that.

I am, however interested to know whether additional (likely 2D) avionics can be added in the free space below the stack. Namely, right below the transponder (see pic). Namely, I would like this to become a real /A instrument trainer, and that means I need DME. I have already added a DAVTRON chronometer and a VOR gauge with glideslope. Would it be at all possible to fit in a King DME unit in the VC? I tried it with the default King DME, but it only partially shows up, and I'm guessing it's a mask issue whereby the mask is covering up most of the avionic image. 

I guess the real question is whether the mask is part of the model, or contained in a BMP file somewhere? If it's the model, I'm pretty sure I'm screwed. But if it's some color thing in a BMP file, or even a config file, I might have some room to play. 

As an aside, I'm also asking if anybody has done black radios for the Cessna 172, and where to get them. 

Thanks.

Attached Picture:

https://goo.gl/photos/oCKWecxHNjyVzcgU8