Ampeg V-4 at 2 ohms?
 

Just got a 70's V-4 today and noticed on the back a switch to toggle between 8, 4, and 2 ohm. Is it safe to run at 2? I don't think I've ever seen anyone do that.

yup.

Good to go. That's why the switch is there. ;)

That switch routes the signal through different taps on the output transformer, so that as long as the speaker load matches the switch setting the output tubes are subject to the same resistance. Unlike with solid state amps, the power output remains unchanged, it'll be 100W at 2 ohms as well.