I double checked the serial# on the machine I picked up yesterday. The actual Serial# is AH590636. This makes much more sense. I originally mis-read the "H" as an "M". The machine is actually a model 66-16 built in 1948, NOT a model 15 like I originally thought. Either way I'm happy, I was just confused at first because of the mistake.
Thanks everyone for the input on the missing cover. Very good tips on searching Ebay. I've always done things the hard way on my searches so it helps me a lot. It's kind of crazy how things work sometimes. I'm looking at paying more for a tiny cover plate for one machine than I just paid for an entire complete machine. I still want the 101 to be up and running though and I've gone through the same sort of thing restoring old woodworking machines. It just means the low "buy-in" price is a good deal, not that the part is over-priced.
I'll be playing with the 66 today to see how it works. Since I've already given the 101 to my daughter it will be an uphill battle to pry her away from it to learn on the 66 instead.