The "B" motor distributor will not engage the oil pump drive gear in a "RB" motor due to it being shorter.The 440 unit can be installed in the 383/400"B" motor if you use the Dc spacer and hold down clamp,as the shaft of the RB distributor is longer.So you can use a RB distributor in all the big blocks if you have the clamp,spacer,and bolt,but you CAN,T use the 383 in the RB motors,mrmopartech