Been there done this and all I can say is "Good Luck" because you are going to find manufacturers who offer supposedly correct for the year applications that are anything but...……………...
One suggestion, don't go with Flowmasters. I have an 85 M/C SS with a small block and the 3/8ths flange ceramic coated headers they offer and claim to be for late G-Body took major amounts of dolly work to one of the down tubes plus trimming of the lower control arm mounting ears on the frame to get them to line up and bolt in. Had I known that they would require the degree of modification that I had to put into them to get them to fit, I would have never bought them. They were a buy now, as I had the $$$ and install later issue and too much time had passed between buy and try. Could not return them so out came the hammers; plus I had to design and have machined a custom shaped dolly to get the dimple in the pipe correct (or close enough for government work). If you have the talent or a good friend that can mig tube, may buy some flanges and ells and make them yourself. More work and time but you will get the fit and clearances you need and have to have.
Nick