Seems like the 60-66 use the same wiper motor and have opposing wipers, the difference is the linkage on the 67-72s attach on a single downward facing lever on the motor, and the 60-66 have a "T" type linkage with the drivers wiper attached below the motor shaft and the passenger above the shaft. Top is 60-66 bottom is 67-72:
I know it's hard to tell exactly what's going on there, but seems like you could just use the 60-66 lever and make your own rods to length. The difficult part is the cowl panel. Now for me, I want to extend the cowl induction into the cowl and maybe only have vents in the cowl scoop itself and smooth the outer parts like they did on some later C3 vettes, would make fabbing the wiper hole easier. I plan on using a vintage air unit so the cowl vents are actually completely irrelevant anyway. I would personally love to get the wipers to stack behind an extended scoop just short of the windshield but don't know if that is possible.
As far as snow, I think it would actually work better, you don't have the drivers wiper dumping snow onto the passenger one. Used to have a friend with an early '70s Mercedes with opposing wipers in Chicago with a foot switch (before intermittents) to turn them on for a single stroke, and they seemed to just magically fling all the snow off the windshield.