This shows the boss for the rare cylinder oiler on the Petter M and the half compression cock thread. Note also the careful blending of the exhaust flange to fit the pot. The holes for the blowlamp bracket have also been twice plugged with studs. The lower set appear to have been a manufacturing error as they have been drilled too close to the flange. The upper set look more recent. The blowlamp itself was only fitted to export models and UK purchasers were expected to use Petters patent starters.
This engine #82859 has another manufacturing error. The piston has the top piston land was reduced to half intended thickness by out of position ring grooves and it subsequently broke out. These errors and the generally high standard of machining (none of the typical tool withdrawal marks) suggest to me that the type was still in pre-production in mid 1923.