When wiring two or more speakers, remember this:
1. The more speakers wired in parallel, the smaller the load.
2. The more speakers wired in series, the higher the load.
There are many resources to determine speaker wiring, impedance load, and power handling calculations. I suggest Googling: "speaker wiring formula"
With parallel wiring, two 8 ohm speakers yield a 4 ohm load.
With series wiring, two 8 ohm speakers yield a 16 ohm load.
Enjoy your new DIY guitar speaker cabinets, wired in series or parallel, or a combination of both!