These engines are really no rocket sience and everybody can learn to work on them.
I basically learned most of tinkering on my WD16H using the very useful contemporary maintenance and instruction manual
and the advise and help from likeminded people.
One thing I usually stress, don't go to modern (tight) tolerances. If you do it won't work as expected.
Think about the average guy of the 30ties wrt tooling and options.
They did wonders with much less tools and possibilities than we can buy nowadays.
Rebore or such "heavy" machining is best done by professionals but the majority of jobs can be done by most people.
A nice general book is "the Vintage motorcyclists' workshop" by Radco giving loads of practical tips.
If you expect a "dealer" to do the job of maintenance for you, I think you should not start with these machines at all.
I have been amazed by modern motorcyclists not being able to check their oil level!
All the practical knowledge you learn will also be handy when stranded at the side of the road!
I have never needed the AA to get me home! Some help from friends was sometimes necessary but I always came home riding.
