How do you set the timing on a 1991 Chevy 454?

This requires a set of special cam hold-down tools for holding the cams in place and the cam sprockets while removing the sprocket bolts. The procedure is quite extensive. Take a look here for a detailed walkthrough with pictures. http://www.60degreev6.com/modules.php?op=modload&name=DOHC&file=index&req=viewarticle&artid=12&page=1 For stock timing you must use the cam hold-down tools to keep the flats on top of each pair of cams parallel to each other. Done one side, turn the engine 360 degrees, then do the other side, so that the left side cams will have the flats facing up while the right side cams have the flats facing down. Good luck!