If I am getting a head that is rated for 60 watts, what is a good watt size speaker cab i should look for so I don't push the speakers to much, is 75 watts a good rating for a 60 watt head?
It should be, heads usually push a bit more than they say they do, but you should be fine with a 75w, i mean, are you really going to turn a 60w head all the way up so its pushing 60w anyway?
A 75 watt speaker will be fine. No worries.
Be careful. Tube amps typically put out 150% of their rated power when turned all the way up. That gives you 90 watts into that poor 75 watt speaker. It should be fine, really, (the AC30 uses two 15w speakers, and they've been around forever) but just a heads-up that if you'll be cranking it a lot or if the speaker isn't well made you could do some serious damage.