You need to drill out that plug. The mixture screw is directly below that brass plug. I bored the plug out with a 1/4" bit (if I remember correctly) until I able to pry the plug out with a screw driver. Hope that helps.
Here are the oil volumes for the 450 Wolverine 4X4: Motor - 2.40 L (2.54 qt) w/ filter change, Final gear - 0.23 L (0.24 qt), Front diff - 0.35 L (0.37 qt). Hope that helps.
