No start on 07 4.3l v6 with spark and fuel.

It honestly does sound like a timing issue. Remember you need fuel delivery, spark at the plugs, the proper air coming into the engine, exhaust flow, good compression and proper timing. Hands on verification of all elements is needed.

You have set the distributor back into the engine in with the shaft in the wrong position!! This is a common mistake on this engine as number one is not at the point on the cap that it appears to be - remove cap look inside - observe closely exactly where # 1 actually is. Let me know if you need more information..