First off, I don't pretend to be an expert, someone may correct me here. First pic is what I have seen on a '71/'72 Blazer and a 69-72 truck for linkage, SBC, with what I call a dogleg upper clutch rod, because it doglegs over. It is used with the frame mount bracket that is straight.
Second pic is stock 292 linkage from a '67 GMC. I couldn't find the upper clutch rod tonight, but it is basically straight. I have seen SBC trucks run the frame mount bracket, in both orientations, with factory rivets, using the frame mount offset bracket, straight-leg swing arm, and the first pictures SBC engine block bracket.
Again, as far as I know you will need the dogleg linkage if you want to run certain types of headers.
Third/fourth pics are what came on my truck, no idea where it came from, other than the frame mount bracket was stock, the other picture shows the frame mount bracket turned around, I can't remember which way mine was pointed. I had a '88 and up block in mine, they do not have the second mounting hole for the factory SBC engine bracket. This was pretty much how mine was hooked up, SBC in the I6 mount holes.
Last pics are of some clutch fork pushrods. You'll need something like these if you're running the stock fork.
Make sense?
Trust me, I've been where you've been, it's taken me a long time to figure this out. Hopefully this helps.