Me again. I just received a set of seven '67 dimes from an auction lot and measured each of them at the indicated location. Got the following measurements (in inches, sorry to my friends in Canada)... 0.0325, 0.0337, 0.0340, 0.0348, 0.0354, 0.0363, 0.0376
Unfortunately, except for the two at the min and max, the remaining pieces are not statistically distinguishable... they could be from either group. I realize that in any case it's a losing proposition to go through all this trouble if you're just worried about the value in silver. I was thinking more for the collector who wanted to fill out his or her collection by having one of each type. This seemed like a possibly valid way to do it.
A note to Rocky. I'm very impressed with the magnified photography. I'm sure you've posted it elsewhere, but if you wouldn't mind, please re-post the equipment or method for producing these images. As for the yellow color, I would venture that any such color is traceable to the constituent copper.