Later models had self aligning rockers and the screw in studs to go with.
Francis, help us out with the vintage 4.3. You may have a great piece that with the stuff Glenn mentioned, it'll be a torque monster. Or you may have the big cam already. Depends on which 4.3 you already have.
Although I'm not a huge big user of Crane stuff, they do have a couple of cams that idle great and will wake that thing up.