I'd say that's a later 1966 first generation 40 watt amp, post "smiley face " logo. Hard to tell for sure, but in the one pic that has the transformer showing it appears to be the smaller tranny.
Look for completed auctions on eBay for one to determine it's current market value, but it's rare. To the right Sunn collector a desirable piece, but it's a pretty limited market.
If the matched cabinet happens to be hanging out in the shop with it, that adds to its collect-ability substantially.
You will need lots of exposure to let that "right" collector find it, IMO the best idea would be to put it on eBay with lots of detailed pics (serial numbers really aren't helpful in identifying old Sunns), give it a nice long run duration and you should get enough attention to sell it for what it is worth; whatever that number may be!
