This is some info I got from Bouchillon:
As per the instructions, If you Have our 4700 bracket (not 7400) , it is designed to work with the 4 groove crankshaft pulley (BPE4013) and the 2 groove water pump pulley (BPE4016). The 2 inner grooves on the crank drive the 2 belts that would go around the a/c compressor and alternator. The 3rd groove out aligns with the inner groove on the water pump pulley and a power steering pump if you had power steering. The outer groove on the crank and the water pump aligns with an Idler Chrysler used on all A/C Big Block Engine.... a single belt went around the idler, crank and water pump and you adjusted the idler to tension the belt. We do not offer that Idler assembly but it can be found on most all older big block Chrysler A/C Engines. We do offer the replacement pulley for that idler assembly.
Most all applications utilize power steering , so we generally do not use the 4th groove/belt out that would have the idler position
Randy Bouchillon
Bouchillon Performance Engineering