You'll need access to a mill, some 3/8" thick material, and a 60 degree drill-mill. Being mill-less at home, I made it at techshop.
Step 1: Square Up the Material and Cut It to Size
Step 2: Cut a Groove and Drill/counterbore the Bolt Holes
Cut a v-groove down the length of one jaw using the same endmill.
Remove the endmill and switch to a drill chuck. Drill through both holes and then counter-bore with a larger bit.