Any ideas what this two stroke 175cc barrel is off

[toucheturtle]

I found this barrel in my father in law's shed. It appears to have never been used but I have no idea what it's off. All four sides appear vertical and it has a central inlet and outlet port.

[toucheturtle]

This is the view from the other side

[L.A.B.]

BSA Sunbeam/Triumph Tigress 175 scooter?

http://en.wikipedia.org/wiki/Triumph_Tigress/BSA_Sunbeam

http://www.hawkshawmotorcycles.com/triumpharielbarrelpics.html