Ammeter to voltmeter conversion

Still learning. My all stock '70 340 Swinger 340 needs some safe upgrades, while appearing stock. You electrical gurus rock. I'm familiar with installing wire bundles, and have an O'Scope, but stuffing a TF 408 in a stock wiring system ain't going to cut it. I've learned a ton of electrical information from all the members here. I bought a sheet of 4X8 plywood to make my own harness with upgraded wire gauge and connectors. More to follow.