Difference between 1967 and 1973 alternator on Small block?
Another difference is the older alternator needs a grounded field mechanical voltage regulator, vs the more modern isolated field electronic VR.
Dimentionally the mount locations are the same. The brackets are unique 69 older and 70 newer.
If you have 70 newer and aluminum 70 newer water pump all should line up correctly ( 2 pulley vs 1 pulley there seems to be a slight difference in CL)
post some photos