As far as I can tell the only difference is that the hoop is slightly narrower so it'll fit on slightly oversized vintage drums. But I will say I've never had a problem fitting standard Remos on my vintage Ludwig kit. Standard Aquarians do not fit, on the other hand.
The Remo Classic Fit Drumheads feature a slightly narrower flesh hoop and step design to address oversized drums made prior to the mid 60s. They are also ideal for older vintage drums that are out of round with thick overlapping drum coverings.
That's how I remember them, too, from when I put them on my Gretsch RB kit. Wonderful heads, anyway.