The "B" motor (361, 383, 400) has one pan, and the "RB" motor (413, 426 W, 440 & that oddball RB383 back in the late 50s/early 60s) has one pan, they are not the same. That valley pan is also the intake gasket and its a one time use item. If its not replaced, they tend to suck oil up between the valley and the bottom of the intake ports.

Last edited by poorboy; 06/26/23 02:57 PM.