Gauge Cluster & Tach Question

[RuralRoute C-30]

I understand earlier clusters, 70's, are not compatible to the 80's. Amp vs volt gauge and the speedo, 100mph vs 85mph, appears to be what visually designates the two besides the volt/amp difference and circuit board differences that exist.

Yet my question is this: Can one take a tach and the smaller fuel gauge from the earlier or any cluster and put in an 80's cluster? Would it work? (think 85...I am)

Seems there are more earlier tach clusters for the 70's than the 80's I see on ebay, so I'm asking, since I am soon back to taking my gauge cluster out once again to update my dash and interior. If I can just swap out my fuel gauge for a tach and install the small fuel gauge where I have no clock anyway, is this an option, or is that circuit board the master controller?

Basically the simple question is: Are the gauges themselves interchangeable except for the volt and amp gauges that are definitely different? Will the circuit board "notice" the difference if I install a tach and a "new" fuel gauge if I leave the other gauges alone?

Figure this question is about as clear as mud so bear with me.

Mark