Jim Snip If the physical mounting surface is the same, then that should work, balancing issues aside. The balancing could be dealt with during rebuild. Any other options? I have had no luck finding a 3 groove, 3 bolt lower pulley. From talking to different people, I'm not sure they made them. Was AC driven off another accessory, like the alternator or water pump, up through 1970? Snip According to the '70 TSM the belt that drove the A/C was the same belt that also drove The power steering pump, or if not used, an idler was installed in the same location a power steering pump would be installed. Thus there were only two belts on the harmonic balancer pulleys, thus needing only two pulleys. There is also an idler installed on the back side of the belt between the harmonic balancer pulleys and the A/C compressor. Your need now would depend on where the A/C compressor you want to install lines up on the crank shaft. If it came from a later car/application you may need the 3rd pulley. If so I think there is no problem in doing a 390 vs 401 harmonic balancer, but would have check on that as I do not know when 4 bolt harmonic balancers were first used and if they are balanced correctly for a 390 John _______________________________________________ AMC-List mailing list AMC-List@xxxxxxxxxxxx http://www.amc-list.com/mailman/listinfo/amc-list or go to http://www.amc-list.com