I run the factory dual row on my early 22R (81') and I wouldn't trade it for anything. It's way more robust over the single row, and a definite upgrade for any motor.
I think it's more of a convince thing, don't have to ever worry about a failed guide again.
Good to know - I realize the older motors run the dual chains. Not sure why Toyota changed to the single chain. I know it is a bit pricy, but seems worth it if I don't have to mess with it again.
Thanks!
