That is a tuff nut. The Guzzi 8 valve motor is noisy. It is not even the same noisy all the time, it is normal for the noise to vary. It is hard to tell normal good noise from the bad noise of failing cams.
There are cases of replaced cams failing. Did you get the replacement solid lifters or the latest roller lifters?
There also has been much discussion about WHY the solid lifters failed. There is nothing wrong with solid lifters, they normally work very well (I prefer them to roller lifters). But the consensus seems to be that the oil system over cools the oil and in cooler, damper, climates that results in the oil not burning off water. That leads to the oil becoming mayonnaise and that does not lubricate as well as oil.
Making sure the oil gets over 212 degrees F is key to a happy motor. I think focusing on that is smarter than fitting roller tappets. Roller tappets do not resolve the actual issue, it is merely treating the symptom.