Recommended hook up for volt meter & oil pressure

First, you did good by getting the mechanical gauge. go out and buy the copper tubing kit for the oil gauge. That plastic tube will leak with any kink, scrape on metal. The wire is hooked to the electrical sending unit for the stock gauge. Remove wire and sending unit. When you unscrew the unit, this is where you screw in the fitting with the copper tube attached, for the mechanical gauge. Plan your route out first, before running the copper tube, so as no kinks.
The beauty of the volt meter is that is in parallel with whatever source you choose. So technically any hot wire would work. Use one that is hot when ignition on, i.e. radio power source, hint.

mine is on the top of the intake, in front of the carb. behind the thermostat housing? I have the EDE rpm intake. so your spot might be different.

no, you're going to want to stay on top the manifold, nearest where the heat is being generated, the heads. taking a look at my intake, the mounting is on the driver side of the intake, right between the distributor and the driver side valve cover.