Whos the 73 up Tach Dash expert?

[Desert Rat]

I have 2 Tach Dashes 1 with a Volt Gauge on with the Amp gauge.I have a 79 Blazer,and it has the volt gauge cluster w/o tach.I want to put in the amp gauge unit becasuse its extremly nice,not the usual junkyard find,but i know i cant stick a amp gauge cluster in a volt gauge truck without some meltdown.Can i swap the amp and volt gauge around and then the circuit board?They both have mechanical oil pressure.Do i have any otions here,the one tach dash that i need in there i dont consider nice enough to put in my Blazer.They both work.the one cluster looks like it just came out of box,other been in a truck sitting for 10 years,some fading etc.Any help appreciated,i know theres someone on here thats a 73 up tach expert!!!