Timing vortec eng code R

having difficulties trying to time a 1998 vortec 350 engine code R V8 . i have tried top dead center with the stationary distributor on the compression stroke with the rotor pointed at the 8 on the dist. still badckfires and wont fire, only cranks, by the way, did head gaskets so thats why it came out, even worse, forgot to mark where it came out, i tried having the rotor off 180 deg than repositioning it at TDC three times. please help!