Yes, I believe that is how the manual says to do it, but I have been told by folks on the oldgmctrucks forums that all you have to do is find TDC, then you can time the distributor. Section 12 in the chevy service manual gives an easy way to time the distributor to the engine if you are at #1 TDC. I can't use the flywheel mark yet because the engine is on the stand and there is no way to attach it. I am hoping to get the distributor timed or at least pretty close, so all I have to do is fine tune when it is on the truck.