I actually looked into this- really, really hard- for awhile. I was prepared to shell out some bucks, too. The people I talked with (MGCycles, Manfred Hecht) told me that the roller rockers tended to break. Too bad. I had a chance to ride a V7 sport built up by Manfred that was totally tricked out- roller rockers, roller bearing mains, everything balanced. It was a completely different feel than any other Guzzi I've ever ridden. Like a BMW...uh..no, better than that, but really tight.
Not to say you CAN'T make a set. It just wasn't feasible at the time. I would still love to find someone who would make them. Then I could buy a set....For my G5.
Edit: btw, when I took my G6 apart for it's too-long-in-the-making rebuild, I did have to replace the cam followers and the pushrods, but the (stock) cam was just fine. This is after close to 300K miles. Dunno what that says about valve train wear in the V11, but I do realize that the G5 is not a high performance motor.