N. C. the motor pictured is a Laura M48.
HS50 is the name of a model of Batavus moped.
The other motor used on Batavus Regency models was the Laura M56.
It is a two stroke that will take 1:25 to 1:40 two-stroke oil to gas.
You are missing the cover on the clutch and the Encawi Carb, the intake and probably the reed block.
You should look at the numbers on the Encawi carb to see if it is a 20 , 25 mph or 30 mph version (or there may be a decal on the frame, nor neck stamp or motor), if you have those set outside of the picture frame.
The tomos a35, a55 seemed to work for the other guy.. with a custom frame mount bracket. (edited)