I recently learned a painful lesson on installing the manifolds on my newly rebuilt GMC 228. While the construction is a little different than that of the Chevy they are basically the same. After installing and torquing them I had an exhaust leak at the number 1 cylinder so I tightened a little bit more and the leak got worse, so I took everything back apart and found I had cracked the exhaust manifold at the outter ear. I had used alignment rings on the intake, but one was not seated properly and found it was bent when I disassembled the manifolds. So I took the exhaust manifold to the machine shop to see if it could be repaired - it could not. He asked if I had separated the intake from the exhaust before installing them. I had not. He told me that was most likely the problem as with the two bolted together it is very difficult to to get them to line up and install properly. He said that the two should be loosely assembled together, installed on the block and then the bolts tightened up.
