Before the intermittent wipers, the upgrade wiper option on C-bodies was "Variable Speed Wipers", which my '66 Newport Town Sedan has. Works well. But I also like the intermittent wipers, too.
As a point of reference, to do a complete intermittent wiper system on a popular non-Mopar sporty car, the whole thing is like $700.00. In any situation, not just something you can bolt on.
I remember the intermittent wiper "adapter" that Radio Shack used to sell. Probably something similar to what Ford used, back then, as the guy that invented the Ford system allegedly got fired as they "took" his design? Seems like that was in about 1968 or so?
CBODY67