To find exact TDC after seeing where the rotor is close to firing #1 cylinder, I always used a cheap ol' piston stop (oreillys uner $3) in the spark plug hole, turn it over by hand clockwise (never with the starter), mark it where it stops, turn it back counterclockwise make a mark where it stops, exactly between the two marks is your TDC. This should also tell you if your balancer ring has slipped. Not to take away from everybodys expert advice, but I had this happen once with the SBC hodgepodge of different timing pointers vs different dampers, nothing being wrong with my new parts but I was using the wrong timing pointer.