Interesting, I have a box of miss matched Pontiac exhaust manifolds. Most are drilled for 6 holes, and all my heads are tapped for 6. Though I have seen heads that were not. I assumed they went to 4 holes in later years but Jim’s 68 only used 4? I’m sure the manifolds are rigid enough to seal ether way. Have also noted that service manuals do not always reflect exactly what the assembly plant did, and that things sometimes could be different at different plants. Go figure. Another mystery?
