From analog to digital gauges ( temp/volt/fuel ) ?

I suspect it may vary with the gauge in question.

Some digital gauges (whether they're the type you're looking at or not I have no idea) get their data via an OBD2 port, which you don't have as it hadn't been completely invented yet when your rig was built. They obviously would not work.

I don't know the answer to your question but...I'm installing a elec pressure gauge and the gauge company Autometer has some techs that were very helpful. They had a "chat" box and provided me with very good info. Not saying they are the best or can solve all. But they provided answers that were not found anywhere else I looked. And free!!