So I guess you are saying that the back of the alternator would hit the head if you tried to move it back. Seems your only option to get away from the 3rd pulley groove would be to move the alternator such that it can move back, it either up or down. I'm using a short water pump and two groove pulleys. The photo shows the alternator aligning with the first groove. This is an old photo, I now have two grooves for all, pump, crank and alternator.Alt sits in front of head/valve cover so nowhere for it to move back unless I reconfigure all brackets.