[JBB]

This part:
Stewart Warner
GGGF X1 (or 666F X1)
1.300 J
Is specific to a solid lifter L-78,L-89,4.10 or higher w/TH400.
It is manditory for a COPO L-72 or ZL-1 w/TH400 in leiu of the fact a 4.10 was standard rear,with higher gears optional. I am not sure of the M-22 or M-21 4 speed application............