66 chevelle gauge help

[scott_fx]

I'm currently in the coding and dev stages of my lcd/analog gauge cluster for my '66 chevelle. The car should arrive next week and it goes straight to the shop for engine, paint and interior. I was wondering if anyone with a '66 could help me out with figuring out the largest gauge that could fit in one of the blank panels like this:
http://www.classicdash.com/shopping/...ank-Panel.html

I want to get a 4 1/4" gauge in there if possible. Would someone be able to help me out with a few measurements?

also. are there any other/better options that i should explore (that isn't too expensive)




thanks,

scott