some Duster gauges not working?

You are correct that the amp gauge is not related to the thermal gauges but...
The amp gauge in a 1976 model has a remote shunt. The small wires to this gauge are in the circuit board harness connector. So this model can have a good shunt and a bad gauge.
Sometimes with a engine R&R the chassis ground from firewall to engine doesn't reconnected. This can cause a variety of problems in different models.
Alt guages is not tied to the ivr in any way. BUT, if you had certain electrical issue I could see the alt guage not working causing the other guages to not work but I would expect the engine would not start either.

Sounds like it is time for an electrical diagram, and a lot of trouble shooting.

So do you guys have any recommendations on what I should do? i don't really know much about electrical stuff, but I would like to at least get my fuel and temp gauges working for obvious reasons.

I do have one question that i don't really know what this might affect but happened when i was doing my V8 swap. so I purchased an ignition kit from Jegs (I will link it) and i did not use the plug that goes into the ignition box because we didn't want to wire it when we already had the original one from the slant six. the only issue was that the slant six plug had one extra hole i guess and the new box had one less prong so right now there is something not getting power from the box. what does this affect? i hope someone understands what i am trying to say.

JEGS 40500K2: Mopar Ignition Kit Fits Small Block Mopar "LA" Engine 273/318/340/360 | JEGS