[72chevynut]

Jason Banks - Using your link and doing a little more searching I found same part number 3929746 listed used on 1970 Ser 10-20 (4/WD), Blazer (4/WD) w/BB (8 cyl.). I'm not sure what the BB stands for here, it shouldn't be big block because the 4WD models didn't come factory with them. My guess is “with brake booster”, would make sense due to the power brakes was a option then and would limit access to oil fill cap.

http://www.gmpartswiki.com/getpage?pageid=220375