Custom digital gauges?

[rally]

So I can do programming enough to build my own digital gauges using a raspberry pi and an analog to digital converter, but what I don't have is an electrical background. I know there's enough tutorials to use a microcomputer to read OBD info, but what I can't find is a pre-OBD tutorial to read our gauges and build a monitor for engine temperature, RPMs, etc, for our trucks using a microcomputer using an ADS1115 for converting our sending units to digital format.

More specifically, reading the tach signal from the distributor (my distributor has a tach output connection, not sure if all do), reading engine coolant temp, etc. If someone could answer my questions about how to step down voltage signals or amplify signals (which the ADS1115 should amplify signals I believe) to prevent frying the computer or allow the computer to read minor changes in the signals correctly, that would be awesome.

I understand the purist POV that I can just install a tach and use the existing gauges, but I'd like to try to build a digital setup others could use if they wanted. Plus I think it would just be cool.

Anyone with an electrical background able to understand how the sending units work and have a rough idea how to convert them to human readable format? Things like voltage ranges, resistance ranges, etc.

I'm currently running an early 80s sbc 350.

Is this something people are even interested in? I figured it might be a fun project. Might take a while though.