what i would do
-buy a 2nd guage cluster
-get the tail tint
-open her up
-spray a THIN, VERY THIN layer over the numbers and junk (they are transparent anyways for the light to get through i think)
so in essence you will be doing what you are doing to your tail lights - tinting over the transparency
i think that if you did the plastic case, it would look really plain and like it was missing something, if you do the guages, it will still have the round circles and look like a cluster just blank haha
i understand you wanna black ur car out and whatnot, but i dont think anyones going to look at ur cluster and say, WAIT A SECOND! UR CLUSTERS NOT BLACK.... -5 STYLE POINTS FOR YOU haha
i just think that your eyes would get tired from looking at the bright outside and then trying to adjust to the dimly lit cluster = speeding ticket IMO.
but i understand you wanna be unique and im just like you are, ill take 10 hours to do something cool like you will
thats actually pretty cool, if it turns out, let us know!