Lauri,
Sew Classic sells a Low Shank straight stitch walking foot for the 66s and other Low Shankers.
http://www.shop.sew-classic.com/Low-...tch-P60400.htm
I've got one on order it will be here this week.
When I did my machine cover for my Singer 66 T-2 I used the ZZ walking foot my wife had for the Bernina. It has an adapter to fit the Bernina but is basically just a Low Shank unit. It worked pretty good even if it wasn't specifically for a SS machine.