I recommend the 175/50R13 for the 13x5.5 and the 195/60R14 for the 14x7, that will go good with 2.5 to 3 inches of lowering in the front and 1 inch lowered in the rear. You could always leave the rear up for the "hot rod" look.

I've seen a late '70 Standard Bug with this combo and it looked great, I wish I had pictures of that car.