I just talked to SPOD and I've run into a snag. Apparently, if you order the switch panel with built-in gauge (which I did) they use a 1.25" gauge, rather than the standard 2 1/16" gauge. They said others have called with the same question and no one is aware of an illuminated 1.25" gauge. If I can find one, I'm good. If not, SPOD said I can send them my switch panel along with a 2 1/16" gauge of my choice and they'll put it into their panel that can handle that size.
I asked why they don't use the standard size for the panel I got and they said it was designed a long time ago. Why they haven't upgraded the design is beyond me.