The worst that could happen is a distributor that is 180 degrees out. At the chev dealer, the service writers would transfer calls back to my phone from hotheads that bought a target eng from our dealer the week before, and it just backfires trying to start. They would convince me that the factory installed balancer was on tdc on timing cover when it came out of crate, so it must be firing #1. THey were mistaken, I had to explain to them that the factory lined up the dots, threw a paint mark on them and were done. And that meant it was firing #6 in that position.