Re: Exhaust plate removal...
If you're talking about the cover on the port side of the motor, that's the outer exhaust manifold cover.<br /><br />All of the bolts in this cover are supposed to be 5/16"-NC, with a 1/2" bolt head. The 9/16" bolt-head sounds like it'd be a 3/8" thread, definitely not supposed to be there!<br /><br />Likely someone broke the bolt in the past, and rather than fix it the correct way (drill out the broken stainless nub and install a 5/16" Heli-Coil), they tapped it out to 3/8". Very Tacky! <br /><br />Maybe they even used some JB-Weld (or similar glue)in there to hold it in place, and that's why you're having fits trying to get it out.<br /><br />Probably the only thing that'll loosen it up is heat. If you have a propane torch, that'd be the safest. Oxy-Acetyl outfit you must be very careful not to melt the alum block!<br /><br />Worse come worse, drill the bolt head off and remove the manifold. You should have better access to the bolt nubbin at that point.<br /><br />Be sure you check the inner exhaust port water jacket cover for leaks/erosion.<br /><br />When you reinstall the new exhaust cover/gaskets, be sure to use a bit of anti-sieze or Permatex #3 gasket dressing on the bolts to prevent future sieze-ups. Also torque the bolts to specs. This is a very critical part of the repair, if the cover is not torqued properly, the potential for a gasket leak is increased greatly.<br /><br />HTH...........ed
I thought I was getting another in good condition for $400, but that's looking less and less likely, the seller is extremely hard to work with. 
