Canuck,
Here is my version. I like to pull all the plugs first. Use a remote starter switch or roll it with the fan. With your finger over the front spark plug hole (#1) roll it over until you feel air rush out. Stop and pull it to top dead center by watching the timing ball on the flywheel through the bellhousing. This is TDC for #1 cylinder. The rotor now points to the area where the wire would go when the cap is installed. Make sure that the distributor adjustment is such that you can move it BOTH ways if needed. As long as #1 is at TDC, the distributor can be moved anywhere as long as 1# plug wire is over the rotor. If you want the distributor wire in a different position, feel free to move the distributor. You must make sure it seats in the oil pump if you do take it out. It won't seat on the block if it isn't in the pump so this should be obvious. I am assuming that GMC's have the bellhousing peep hole for the timing mark.


Stuart.