Isn't the 7345 a pyrometer, not an A/F gauge? Either way they should wire up similar, 12v keyed hot wire, ground, lighting, and if an A/F a wire to the 02 sensor, if a pyrometer a probe into the exhaust manifold.
I had an A/F gauge in my 75, but during the winter I replaced all the gauges with cyberdyne digitals, eliminated the A/F as it was only a narrow band and pretty much useless for anything but a light show. If you want an A/F for tuning or accuracy go with a wideband gauge and sensor. My old 75 didn't have a factory 02 sensor so I just welded a bung into the collector, mounted the 02 sensor, wired it up, I used a 4 wire 02 sensor, they are available as a 1 wire, 2 wire, 3 wire, or 4 wire depending on what type and style you want.
I run their #5775,was advised by LC to run one as Toyota's want to run rich. This is a non stock engine! It wired up pretty easily, just be careful as the wires are real small,solder all connections & use shrink wrap!