alternator belt alignment question

[Ken Keith]

Apparently, I need to figure out some combination of pulley and 
washer orientation/omission to get my 110a alternator to work 
correctly on my '88 5kcstq.

I don't really feel confident in my ability to "eyeball" whether the 
belt is straight or not.  Is there some better method to measure the 
alignment between two pulleys?

I can put a straight-edge inside the groove, but I don't know how to 
make sure that it is exactly where it should be.

Thanks!

Ken