Frozen bolts in cast iron head

[EML]

Now I see the problem-get a hoist and put it in the air. Then all will be revealed.
This will be an on-going problem for the car if you don't do it right.

[GMC]

Don’t even bother wasting your time with easy-outs, they will only give you more grief. They can be good for bolts that happen to snap for no real reason but anything that is frozen in they won’t be able to budge as the torque needed to move a frozen bolt will be greater than the tensile strength of the easy-out.
This is also the problem with the bolt’s, they deteriorate over time, especially around exhausts, so the torque needed to move a frozen bolt will be greater than the tensile strength of the bolt itself.

If you can get a spanner on them just turn them till they break.
Use a cold chisel if possible, welding onto them can be good but that usually only works if the head is rounded, if the bolt is frozen from shitty threads then it is most likely the remains will snap.

Once you get the manifold off then find yourself a right angle drill if necessary and drill and re-tap them.

Once you drill out the centre, the remains usually start to fall out and tapping them becomes easy.
I have also seen left hand drill bits for this, it drills them out and if the drill happens to grab then it will undo the remains.

Spend your money on quality drill bits, starting with a pilot hole (small) which you can drift around if necessary to drill in the centre.
My preference for pilot drills are ‘Shortie’ No 20 or No 30 drill bits by Sutton
Short drill bits flex less and help you stay on track, also use a lubricant on them to keep them fresh.

[crash n bern]

I could cut the exhaust off, pull the motor out and just drop a 500 cube crate motor in

If you do Bernie, can I buy your Nail Head engine ?

It's not a nail head, its a later 455, but it is a GS motor with stage 1 heads.  The cars a dead stock, matching numbers, fully optioned (Except for column auto and split bench rather than buckets and T bar.) 72 Buick boattail Riviera. I was only joking about the crate motor, that's something Chip Foose would do.

Some good advice there GMC, I was only joking about the easy outs as I've never had any luck with them.   The bolt that did snap, snapped very easily, like butter. Fortunately there's some thread hanging out the other end.

[pancho]

 Two comments- if you use brass or stainless nuts they very likely will continually come loose. Correct exhaust manifold nuts have extra thread clearance and are less likely to sieze on and rarely come loose.
 The trick with drilling out broken studs is that you MUST get the pilot hole dead centre other wise lots more trouble. If you can't guarantee that, ring an expert mobile pro.
Remembering that removal of broken studs in a V8  doesn't have easy access.
 cheers pancho.