Howard, interesting question. I havent converted an existing brake to hydraulic, but I did fabricate an entire 4 leading shoe hydraulic drum & wheel set up for a side car outfit in the early 80s. I used 2 Triumph Herald front drums & brake plates mounted onto a steel disc centre with a 14" Morris Minor rim welded to it. A Japanese M/C master cylinder was used to actuate it all. Dont even know what size the cylinder was but it worked well with moderate pressure. Was extremely heavy of course.
This was all in exchange for the genuine ex Egli Grimeca set up which graces the front of my Egli replica.
Why the interest in hydraulics to the Laverda wheel? Is the current lever action too heavy & short of feel? The old 4L/S Guzzi wheel on my Sport is possibly one of the most maligned drums built, all the road testers bagged them for being heavy & having the feel of sqeezing a 4x2! I have learned to exploit it, it is a very safe brake, difficult to lock, but can be warmed up, the oft discussed "servo effect" felt & the tyre made to squeal controllably with practice. It has 500 lbs of bike to slow without my weight being added. I believe it could be "improved", given more feel & less lever pressure, by changing the bar lever fulcrum. This may be an option for the Lav brake if this is the issue. There was some good articles in MPH a few years ago detailng brake lever fulcrum points, may be worth a look if you can track them down.
Cheers, R