I think the only ones that bolt up are the Morana V6 Racing ones. Pat Norris had a set of roller rockers for his Vulcan, though I can't remember if he installed them or not. I don't think he got them from Morana either.
I've heard that, and I've also heard that Morana's fit right on. The ones Pat had needed to be machined in order to use them with the stock pushrods. Otherwise, different lenth pushrods are required to retain valvetrain geometry.