When you put that top end and cam in did you degree the cam? If not your cam could also have some additional advance in it adding some compression during cranking. Also as Todd mentioned if your ignition timing is to advanced then it will cause cranking problems for sure.
So bottom line did you double check where TDC is and cam timing then drop the dizzy in knowing it was close or just use the marks on the cam gears and balancer? Those marks aren't always accurate, that may be your problem.
