I machined mine out of aluminum. Well first I made a hinged one out of 1/4" steel, didn't like it. Then I made one out of 1/8" aluminum, but it flexed. Then I made one out of 1" aluminum. It's actually 3 pieces, hence the countersunk allen head bolts:
Not sure if you need the locking pin too? i did my HG a bit back on my m44 and created the jig for cams and had a machinist make the motor locking pin to spec.