YES!! If it's in working order $500 is a steal.
The 15" ones were targeted at the steel/lap-steel guitar players. But are awesome none the less.
Probably gonna be the best clean sound you've ever heard. If memory serves, 1968 was a transition year with some being 'blackface' and some 'silverface'...not too sure though. What's the one in question? Blackfaced is the more desirable.