Need help '68 F-100 360ci

The left(driver's side) exhaust manifold is cracked. This truck was ordered new with "Ranger" package and all options, so it has the factory
installed A/C. There's a bracket from the A/C compressor that goes down and bolts to the top of the exhaust manifold. The replacement I got had correct casting number, but doesn't have the hole drilled and tapped for the A/C bracket in the square "boss" on upper side of manifold. Does any one know the correct angle of the exh. manifold mounting surface on the head, in reference to verical? I would need to know this to set up a jig to hold head at proper angle, then drill and tap a hole in the vertical plane. Also, I know I'll probably have difficulty with at least one bolt when removing them for replacing the manifold. Any gotcha's or advise to make this process as painless as possible? I REALLY don't want ot have to pull head because a bolt wrung off! Thanks, in advance, JR in N.C.
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JR wrote:

Hi JR, Cracked exhaust manifolds are real common on FE motors (352,360,390,etc). If your truck has been in NC or the South in general all it's life, you may have a chance. I'm in northern Ohio, the rust belt. These days I pull the heads on FEs any time I have to replace an exhaust manifold, due to past experience. The bolt holes are "through holes" and the bolts protrude slightly out of the holes. This allows moisture to wick back into the threads causing rust. Of course, try a couple of bolts first, they "might" come out.If any appear to be frozen and you don't have an acetylene torch, don't even try it without pulling the heads. Whatever you do, work slowly and patiently. One method I've found that sometimes works; Heat the bolt head with the torch until it's red, don't heat the manifold casting. Quench the bolt with water. The thermal shock will often break the bond in the threads. Apply liberal amounts of penetrant to the exposed threads(PB Blaster is the best IMHO). Do this abpot 3 times and try to remove the bolt. A 3/8" impact with a 6 point socket can help break the bolt loose. The hammering will often loosen the bolt, where steady pulling with a wrench will snap it off. Replace ALL of the bolts. The old ones can be brittle and break when you install them. That'll really make you want to cuss. I know you don't want to pull the heads. I've found that,for myself, it saves time, aggrevation, and possible damage to just bite the bullet and do it. Then I can clean them up, and inspect the inside of the engine too.         Good luck, Tom
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