2" to 2-1/2" filter will work, but not enough air for a 400-455. Even a K&N would be borderline in this case.

My thought as well. I'll baby it until I get the hood cut open and the scoop mounted. Then a 1" spacer, a 4" K&N with a filter top and some version of a 68 lower pan setup to keep the hot air out if it works out.