DPMS Hi-Rider upper

I posted on the DPMS forum and didn't get a response so I figured I would ask here. I purchased a DPMS Hi-rider upper only to be used in a target rifle build. I have a barrel coming and the Model 1 vise block I have for the A2 and A3 doesn't fit the upper. Is there a special block available or should I get out the dremel and modify the one I have? Any help would be appreciated.