I bought a PP balancer and the keyway was to small for the key on my Magnum 5.9 with a 408 stroker.
Having the keyway machined to fit. Not cheap to have done.
Just wanted people to know surprises are waiting with magnums.
Oddly for me, I didn't have that problem. The balancer went on smoothly with a balancer install tool. I took it off once too and it was fine going back on again. Unrelated but I realized the oil slinger wouldn't work with the cloyes chain and mag timing tensioner (reason for removing the balancer).
As for the other suggestions, I am going to go with my gut and the suggestions here to use 91013 and see what happens. Its really the only one that makes sense to use.