Ah—I had thought he’d sung “drinking whiskey an’ rye...”
No way to know for sure. Maybe some of his wording is just words that rhyme and sound good together. McLean isn't saying.
Saying "drinking whiskey and rye" would be like saying "drinking beer and pilsner". Since pilsner is just a type of beer, just as rye is just a type of whiskey, it doesn't make much sense. Again though, it doesn't preclude him saying it if he chose. The lyrics to the song posted on his website DO say "and", not "in".
I just prefer the explanation that seems to make the lyrics logically make sense. It makes more sense to me than pulling a phrase from some Dinah Shore Chevy ad that mentions a levee and throwing it together with some unrelated phrase about drinking whiskey and rye. I think McLean spent a lot of time choosing just the right words for his thoughts and that he didn't throw in words that didn't make sense in portraying his thoughts.
Other things in the song like "sang for the Kind and Queen" don't make sense until you look on the internet and find that there is a King and Queen pub in London where Dylan played. In "a voice that came from you and me".... check out youtube versions of Woody Guthrie singing This Land is Your Land and you'll get an idea what Dylan used for creating his singing style.