We can help you figure out what the motor is and what year, if you want. First, does the water pump have 8 bolts in the front or 11? If it's a 67 or 68 setup it will have 8. 69 and up has 11. Basically you need to match up the pulleys from one setup, as you figured. There should be part numbers on the pulleys that can be used to figure out what they are from assembly manuals. Maybe just one needs replaced, maybe start fresh with a matched set.

From the pic it looks like you at least have the correct 67-69 alternator/power steering brackets.

I'm guessing, but you may have a 69 long snout water pump with a 69 short snout pulley. That would cause the water pump pulley to be 1/2" too far forward. I've dealt with this on 69 GTO's