Finding Top Dead Center on Chevy and Other V-8 Engines

Assuming the direction of the rotor was marked on the engine prior to distributor removal, when you drop the distributor back in, you need to rotate the rotor ahead (clockwise) roughly 10°-15° to compensate for the spiral gears. It will turn back to its marked position when it is fully seated.

…If the engine was disturbed, the valve left cover needs to be removed and the engine turned over SLOWLY so that you can observe first the exhaust then the intake valve close on the #1 cylinder (#1 is the front cylinder on left bank, intake valve is the 2nd valve back on #1, exhaust is 1st) then align the timing mark on the balancer to the TDC point on the timing gauge on the chain cover.

Next, the oil pump slot needs to be turned to align with the tab on the end of the distributor shaft (the tab is aligned with the rotor). Finally, identify the #1 plug wire on the cap and point the rotor toward that direction but ahead (clockwise) roughly 10°-15° to compensate for the spiral gears. It will turn back to the #1 position when it is fully seated.

This should allow the engine to start after which the timing can be set with the timing light.