Linked are two pictures, the first method I used, aluminum bore split, then clamped over gear by vise, use big adjustable on the web of the crank, gear will rotate with reasonable force. I made a set up that used the side cover bolt holes, an block made from a quartered cam gear turned inward, this was then forced with a threaded adjuster. I could change cam timing on the dyno with out removing the crank. That tool has been sold and I did not rebuild it.
http://s24.photobucket.com/user/meaded/media/torqueplate.jpg.html?sort=3&o=0
Also on one of the engines on the bench notice the torque plate, I simply bored through a cylinder head, it replicates the bolted on head as accurately as I can imagine.