66 - 1001 is the model of the watch. It was made by Seiko approx 1968-1971 - not sure how many were made...
Well, "66-1001" is a legitimate style of case code# for that time period. Just one wrinkle ... the Seiko movement table shows the 66A & 66B only coming in a 17j variant, the pictures posted here show 21j on the dial. The only related calibre (hand-wind) with 21j is shown as the 6660A, but then a "66-" case code does not make sense. Here's the entry from the table for the "66" calibre with jewel count underlined:
66A,B Hand wind Sportsman 17
1960 S 10
If there are jewel count variants, the table shows the range. BUT: The table could be wrong, I don't guarantee it's accuracy.
In web searches, I did find a link that supposedly shows a 66-1001. Unfortunately, I'm not a member of the forum the link is on, so I can't view the posted images. If you're interested, you can likely join & see if the "66-1001" pictures shown look like what you have:http://www.thewatchsite.com/21-japanese-watch-discussion-forum/38768-what-s-top-10-rarest-valuable-most-desired-seikos.html
Look for the entry by "uswatchguy" in the thread with the following text & the images posted:
"Here's two you probably never heard of, because there are two (repeat 2) only known examples in the world. They are the 66-1001 models. One is a 14k yellow gold case and bracelet mechanical watch and the other is 14k white gold case and bracelet automatic watch. Both were produced in the late 1960's by Seiko."
By the way, what "uswatchguy" says about the 2nd example (being automatic) makes little sense to me ... the "66" only came in manual wind. There are derivative calibres in the "66" family (like the 6601A) which are automatic, but then Seiko would likely have a different case style#! So, I'd be a little cautious about his statements! Too bad I can't view the pics