Pulling original 454 exhaust manifold off

[BoxMasters]

Hi, the local shop tried to take off the exhaust pipe from the original exhaust manifold and two of the three bolts broke on each side. 4 of 6 bolts are broke.
A muffler shop said they can replace the exhaust manifold bolts if I remove and bring them the manifolds.

SO, I need advise on removing the original exhaust manifold to try to keep from breaking a bolt that hold the manifold on the engine.
The truck is a 1991 Suburban 454 2500 TBI w/ stainless factory exhaust.

I do not want to break a bolt off the engine!!! HELP