"This bike showed up at my local Salvation Army store today and I couldn't pass it up."
You'd be kicking yourself if you had, that's for sure. You've found the needle in the haystack there, amigo. 10 speeds, even top line ones, became fairly common in the US during and after the 1970s and they pop up in thrift shops. However, a derailleur bike would have been a rare bird indeed on US roads in the 1950s and for one to make it this long and then go to a thrift shop? I'll find my Masi or Cinelli at Goodwill before another of those Raleighs show up.
Clean it up and hang it on a wall. If you do sell you'll be happy with your return. It won't set your retirement mind but put it on eBay or something with wide coverage and it'll make you
. Personally, I'd keep it even if it doesn't quite fit. The money will be spent on something else sooner or later and then it and the bike will be gone
.
Congradulations.