I'm guessing anywhere from 75-100 wpc RMS. Ya know, unless you are running mega-wattage, you'll never blow a speaker unless you're playing it at herculean levels pushing your amp into clipping. If you are looking for a PA speaker, don't bother with most any home speaker brands. But if you are running a mid-fi brand reciever or amp, it should do nicely. These types of speakers were usually rather efficient, so as long as your amp provides clean power, 50 watts will do. Since this an old speaker with (I'm guessing) 6db x-overs w/ 35yr old+ 60v-70v electrolitic caps, I'd play it safe with these things and just enjoy them for the novelty that they are.
I am not planning to use them. I got them from a friend and I am thinking to put them on craigslist but the stickers are not on the speaker so I can't just put them like speakers for sale. That's why I am asking