[Congrats! Definitely a 66, three years older than mine... That missing throatplate is common and you can buy a replacement on Ebay. It will slide on from right to left, under the presser foot. I know of a YouTube that shows you how, if you happen to need it.
You got a great machine. Can't wait to see it again after you clean it up]
I found the throat plate. It was in the box with the attachments. I'm anxious to get it cleaned up.