I did solid mounts on a friend's 1200 and couldn't hardly stand the vibration. I still have that set of mounts here. It didn't make sense as so many of the Cub cadets run a solid mounted engine. I wound up getting a sway bar link for a Rwd GM car and used the bushings out of it. The heavier duty urethane version. That made it tolerable at least. I think there is something up within that engine but it continues to run OK and no smoke so the owner is putting up with it for now.
And this is exactly what concerns me on doing mine, I've heard about the BAD vibration issue before, thought I would try exactly what you said you did with the bushings from the short strut-rod that holds sway bar on big GM rwd's. I can get original GM bushings for WAY less than Cub parts but only a little less than the "solid" ones. Guess I'll just bite the bullet...want to pass on your solid ones (reasonably) ?