I would say it would be an early (late 67-69) block. I bet the water pump also has the inlet on the passenger side, and it probably has a 3-bolt front balancer. Yes, there were some blocks made in late 67 as 68 year models.
Some time in the 80's they changed from two peice rear main seal to the one piece. I know the 85 GT I had was a one peice rear main seal and the pionter was on the right side but, what was the first year I'm not sure.
Thanks for the replies, it is not a big deal as far as getting the car ready to race. I am just going to make my own timing mark. It was more out of curiosity. Thanks for the help!