Woog, there is a slight difference on the distance on some heads, I don't know which engines or the year models, but some exhaust manifolds have to be doctored a little with a drill bit to get in the front and rear bolts. But, anyway, the holes in header flanges are probably large enough that they will probably fit any sbc (maybe a little file work may be necessary) so, when you have your headers installed and your fitting bolted to the end of the headers, your best bet would be to take it to a muffler shop and let them go from there. Probably will be as cheap as buying all the parts and then having to install them and the job will be neater and you won't have pipes and mufflers bumping the frame, cross member, shocks and wearing holes in your brake, gas, and automatic transmission lines. I do most of my work, but there are some things I usually don't fool with. Windshields and exhaust systems are two to name.
Truck Tinker, have a good day
