Hi.
The G20/19 (like many other S.T.) has undergone many changes over the years.  The first edition had the head made of casting, the piston had a baffle and two rings, the shaft was supported by a rear ball bearing and a front plane bushing.  The various modifications resulted in an engine with a machined head, a flat piston without a ring and two ball bearings.  I have no information regarding S.P.I.  but I would not rule it out especially in the first versions, the big brother G20/23 originally had two small open corners at the base of the exhaust port with the piston at the TDC.

Massimo

Back in about 1949, I owned a Super Tigre G-19.  It was .29 cuin with a sand-cast crankcase.  It's main feature was an exhaust stack on each side.  I think it had ball bearings, but not sure.  I believe it was intended as a racing engine, although I used it for free flight with a 10 inch prop.  So it never got overr 9K RPM.

It was just another engine to me, and I later sold it for next to nothing.  I now realize my mistake!