i wouldnt go any further then you have gone. like jd4242 said, you dont want to weaken them, just make them the same.
DOOOOOOO IIIIIIIT!!!! go with the JBA's however. heard nothing but good about them. also, spend the extra $$$$ and get them coated. that way, in winter when they throw enough salt down on the road to kill a cow, they wont rust, or as fast. you may also need to tell them if you have a internal, or external EGR system.
look closer. they are for a SBC :scratch:
i think most headers wont come with a Y pipe, as they normally....and i stress the word N O R M A L L Y bolt to the stock y pipe. unlike the "true fit headers" that i have had to deal with in the past where you have to smash them in several places just so they clear.
if your going to order headers don, grab some good gaskets, as well as bolts for them. you will thank yourself later.
edit : or grab the ones that jd4242 found. didnt look to see if the same company had them.