Timimg Question

[1986Silverado]

The 85 Silverado that I drive to work seems to lack power when the go pedal is mashed to the floor and it also rattles......valves that is. It has an older 350 in it and seems to run good until the gas pedal is mashed to the floor. I am thinking the timing is off. I have not checked it. I have read that base timing at idle needs to be around 10 to 12 degrees BTDC. And forgive me for the stupidity but if I were standing in front of the truck looking at the damper trying to set timing where is BTDC to the left or right of TDC? Or another way to look at it is above or below if looking at the damper from the drivers side fender? Been awhile since I've owned a chevy that I have had to work on. Thanks!