There were several variations in the "Blue head" Super Tiger G60. Including the flat top piston.

Anymore with their age, it's sometimes hard to tell if a person is running a plain G60, or one of the Blue heads? The blue fades away with use.

The current ST GS40 has, what one might call, PDP ports added in addition to the usual Schnurle ports. Some people would tend to call these PDP ports but it's really just a 6 port GS40?

Enjoy,

Jim