The only difference I can think of would be the hole for mounting the bumper. In either case, the hole could be filled and repositioned for bumper height.
The turn signals don't enter into the picture as they are mounted in the front valance.
I had to use a late front valance on my early car since at the time, they were still NOS and not being reproduced. I think I bought the last one TRF had in stock. I don't remember there being that much difference in the hole heights.