ORIGINAL: DarZeelon
Flyby,
From its external appearance; this engine seems to have a classic Schnürle porting arrangement, as originally introduced by Adolf Schnürle.
I.e. there are only the two angled side-ports; and the boost-port nearly all Schnürle ported engines now have, is not there (although it could be ground into the sleeve, but I doubt it).
The boost port is behind the HP 61 label. It is small by today's standards.