Here is the factory spec. It is indeed 50hp sra-moteur.com/uploads/catalogue/produits/documentations/md22l-md22l.pdf always was in its basic form (22L) which was fitted to your boat when new. However there was also a P spec which was 59hp fitted to some of the larger Bavarias and a TMD22 (turbocharged) with 78hp, again for larger boats.
The basic engine is a British Leyland used in such cars as Montego and Maestro plus taxis and LDV vans. Reengineered as a diesel by Perkins and then marinised by both Perkins and Volvo.
Like many diesels power outputs can be varied easily by either governing maximum revs or by adding a turbo. The basic MD22 is low output for its size and unstressed which is why they have a reputation for long life.
Hope this helps