My vote is also 19's in the rear and 18's upfront. Also makes brakes look bigger.
I even like the 18's in the rear and 17's up front, i know, i know i need to step into whats-in today, i guess still a little old school still in me, but i personally like this look on a 67 and 68. Also makes the brakes look bigger if your running 13" rotors.