1997 GMC Yukon

I recently did a cylinder head repair job at home to fix coollant in the crankcase problem. I believe now that it must have been a blown head gasket coupled with poor factory milling on the left bank. After reassembly I seem to have a timing problem that will allow the engine to rotate very fast and not start. I have eliminated the spark and fuel as being the problem. so now my attention turns to the timing and compression. What could I have done that screwed up the timing or compression that bad. Could it be valve lash?