On the first question I'm not sure, but I think there is a felt washer there to help keep dirt out. Question 2 my Z bar as in figure 3 on my 63. I doubt there is any difference. When it's installed correctly it sits pretty level. If installed wrong it's at a bad angle.

Larry
68 C20 327 daily driver
63 C20 292 Camper truck
65 C10 ? Custom Cab AC,PB,PS,$flasher


I don't own a vehicle that isn't old enough to drink.