The B4 used imperial bearings, the 4.1 uses metric and also has a new gearbox case + T plate. You only need the newer outdrives and bearings to convert the B4 diff itself to metric.
B4 bearings - #6903 (3/8" x 5/8")
B4 outdrives - #7667 and #7668
B4.1 bearings - #9832 (10x16mm)
B4.1 outdrives - #9852 (pair)
