Another ES-345 Wiring Solution:

I recently bought a 1964 ES-345, and figured I'd re-wire it for mono. I'm aware of the "ES Box" adapter, but until I made up my mind which direction to take, I simply bought a "Y" stereo cable, a plugged an end into the separate channels of my Fender Deluxe Reverb. Holy crap, I will NEVER re-wire this guitar!! Run like this, you get volume and EQ'ing for each pickup separately. Amazing!!!

This is one of the the standard solutions. The intended use is with the old Gibson Stereo amp with a stereo cable - but any two channel amp will do!

A fine and funky variation of your solution is to plug both ends of the Stereo-Y-cable into one channel of your Deluxe Reverb. This will get you the funky "out of phase" sound when using both pickups.

The ES-Box acts exactly like a Stereo-Y cable but allows one to plug into a single channel amp. It also preserves the OOP sound.

Welcome to the ES345 club. Your initiation has really only just begun. There is more...much more...

Another Y-cable thread: https://www.lespaulforum.com/forum/showthread.php?173138-Two-Photos-of-My-Three-Electrics-(Some-Vintage-Content)-BIG-PIC&highlight=a+few+pictures+es+345+boogie

A recent OOP discussion (applies to ES345s too): https://www.lespaulforum.com/forum/showthread.php?212177-Peter-Green-Les-Paul-tone

Also, upstate NY? I was in Albany for a few years... Are you familiar with Super 400?