´68 BB vs SB K-Member difference?

So I took a look in my DC Racing Manuals, and sure enough. Three different BB K-members for A-body.
´67 K-member PN 2881925, ´68 PN 2883984 and ´68 w/p.s. PN 2883999 ´69 PN 2883999
The DC piece P4007935 has spool mount, so not really an adequat comparation here.