Pinrepair website has lots of info about cloning Hs40s.
The short answer is yes, you can do it, but will need other Hs40 specific parts to do it.
You'll need a skinny flywheel and starter cup for the skinny shroud to fit.
You may need to install points/condenser, a lot depends on what year your Hs50 is.
I have cloned a couple myself, if you do a search there is lots of info here