Need help on a 1968 Inline 6 250 Engine

[RichardJ]

If you are trying to make it original as in how it originally came from the factory there are a few problems in the photo.

There are eight, course threaded (3/8-16 NC) holes along the mounting surface on the head.
That first hole should not have a threaded stud. There should only be an unthreaded locating pin protruding above the surface. It threads into the head, but the only part visible, sticks out about 1/2" and is about 5/16" in diameter. The same locating pin is used in the last hole at the rear of the head.
There are only two threaded studs used on the head. The third hole in from the front and the third hole in from the rear. The stud is about 1 7/8" long. It has the 3/8 - 16 NC thread for screwing into the head and 3/8 - 24 NF on the outboard end for a nut.

The other four holes in the head use a 3/8 - 16 bolt.

There are two different type clamp pieces used. I've had headers on my truck for many years and I cannot remember how many of each of the clamps are used or their location along the manifolds.

You have a smog head in case you were wondering what those internal hex plugs are, that are above each of the exhaust ports.
That's either the wrong head for your truck or your truch should have the A.I.R. Smog pump un it.