Nice that really helps, I actually forgot to mention that it had the ceramic coating also. But the method with the other pipe wrapped might be the winner. But if I have to taper the hole,what could I do about that spot that wouldn’t have any of the ceramic coating after I taper it.You can either give the tube a little squish on that side, or take a rat tail file /die grinder and carbide burr and taper the entry side of the hole to the outboard side....it won't take much to get enough room for the bolt to slip into place....you'll just have to remember that bolt has to go in either first or with the header still really loose on the bolts so it can be pulled far enough away from the head to allow the bolt room to tilt into the hole.
If needed you can also get header bolts with a 3/8" or 5/16" wrench head instead of the standard header bolt 7/16" head if you need more wrench clearance.
I had two tubes like that on my 1-3/4" SBC Hedmans for '68-74 Nova/'67-69 Camaro...I took a 3/4" diameter piece of thckwall tubing or solid stock and wrapped it with a few layers or electrical tape, then laid the wrapped tube against the side of the header pipe and smacked it with a small 5lb hand sledge hammer to put a nice curved dimple in the tube.....that way it looks like it should be there, rather than like you went postal on it with a framing hammer.
This was with ceramic coating too, you can do small adjustments like this without hurting the coating if you do it prior to running hte headers for the first time....the coating needs exhaust heat for the final cure.
I know the flange is pretty thick but would that cause an exhaust leak in the future with the taper having to be in the header pipe?I would grind the hole on the flange mounting side with a small carbide burr so the threads clear as slide in. Grind so you create a slide taper to that side of the hole only. You will need to start this screw to the head first when mounting. No evidence of rework once installed.
okay let’s say I take a little off both sides of the flange to minimize the amount taken off on 1 side. What could I use to protect the area the ceramic would be removed from.I fact maybe just grinding the bolt shoulder where the hex flat is might do it for you.
If this were my project this would be my first attempt. Always go for what seems to be the most straight forward solution. But this would still have to be the first bolt threaded into the cylinder head. You may still be limited to using an open end wrench.
If you remove material on the head side , you will narrow an already limited area between the bolt & exhaust port , I'd rather see material removed on the frt side rather than compromise gasket sealing ..Only one side the side against the head. Not visible once mounted. The shoulder on the bolt would be as I said my first choice to grind down.
Are you familiar with hex socket cap screws? That may assemble with out grinding at all. Head is very small, suggest use a washer with it to spread clamping force.
If you remove material on the head side , you will narrow an already limited area between the bolt & exhaust port , I'd rather see material removed on the frt side rather than compromise gasket sealing ..
This would be the way I'd do it to if grinding the hole. If you go easy with the cut, no exposed metal will show when installed, and just touch-up paint to to prevent bare metal from corroding in the hole.Header paint ..