If you are going to get both gauges to work, you need to systematically start at the beginning of the system (circuits) and follow it along , either identifying problems or eliminating them.
Having the wiring diagram is a good idea (see Technical Resource Library).
1) do you have voltage at the Constant Voltage Regulator?
2) does the CVR work correctly? (fluctuate from 12V to 0 V, averaging 6 V)
3) do your gauges work? (ground out, very briefly provide power, see if the needle jumps)
4) do the sending units work?
a) does the Temp sending unit vary in resistance as
the surrounding temp changes?
b) does the Fuel sending unit vary in resistance as you move the float arm?
5) do you have good grounds at the each sending unit? Have you done cleaning and grounding?
This only takes a multimeter and some lamp cord sized jumper cables.
You can thus comprehensively check out the entire system and know what you have, as opposed to changing things and hoping to get lucky.
Depending on the problem(s) you identify, you can
* get new CVR or make your own
* get your instruments overhauled, calibrated
* buy new sending unit(s)
* install your own grounds
and in the process, develop methodical approaches that pay off repeatedly on the ol' car.