Pulling original 454 exhaust manifold off

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