Here is one of the former OEM suppliers to GM, check out the 5/16 fuel Ys, and guess which ones they used.
http://tubingandfittings.eldonjames....ngs?&pagenum=3
I got the SS model and port/flowed it with drills and will never have to touch it again. GM owners got the 1.61 specials....that GM probably paid 25 cents