Yeah 1.5 is about an inch over stock...they don't look bad but i would get a 2.5 before i'd get a 1.5. Then again i'd probably get the heat extractor before i'd get a cowl too.
I say stock, my newest addition has a 3" cowl and it's ugly imo. Problem I have is it's required to clear the 351 with Edlebrock intake. So I'm stuck with the cowl hood or I have to go with no hood at all.
If it clears, stay stock. Cowls just look too heavy.