Thanks to the FW history book that came with my recently purchased FW, maybe I can help a little here.
The 221KS was probably built in Clydebank in Scotland. It is believed that the machine was started in Scotland at the Singer factory there and then sent to Canada for the motor and footpedal (or perhaps more) to be added. Canada and USA have different electrical needs from England so the Canada factory (St Johns, Newfoundland) finished the ones to be sold in N America.
The 221J was definately made at the Canadian factory according to my research. Both of these machines were birthed in 1960-61. You said you were able to track these down to 1961 so that's good.
The AH53683 (straited face plate?) was birthed April 20, 1948 and was made in Elizabeth, NJ, USA.
The tan or white machines get more money than the common japan black. There were around 3.5 million FW made but they aren't making them anymore so even though the values are down a little, they are still a great thing to have and people are still looking for them. You should get more $$ if they are working so be sure to try them all out. They are a little picky about how they are threaded so be sure to check out the books that came with them. I thought my first FW was broken because I didn't have a book and threaded it wrong the first time I tried to sew.
I have 3 black FWs at this point but don't have a white/tan one or a 222 so I'll still keep looking. Please let us all know what you decide to do because, I too would like a chance at one of the white/tan ones you have.
Good luck!