I concur with Edd. With repect to your admitted engine novitiate status, be smart. Apply KISS. Buy the O.S. and avoid frustration. If you want an engine virtually guaranteed bolt in, flick 'n fly friendliness, the O.S. .61FX offering is the way to go and definitely worth paying for in this instance. Alternatively, specifically for a PT-60, have a look at the O.S. .65LA. Great value, sufficient power for what you want to do with a PT, reliable, and very user friendly.

As for the ST, do an RCU search on the endless reports of ST tuning woes. 'Nuff said. If you go the ST route, there's a better than even chance it'll all end up in tears, and expensive 'tears' if you deadstick and write off that shiny new PT-60 in an unnecessary forced landing! We all like to save, but it's also important to triage when an apparent saving mght be a false economy.

FTR I have both brand engines in a .61. A current O.S. 61FX and an Italian Super Tigre S61K ring, which is the immediate predecessor to the current G61 ring. That ST .61 differs from the current ringed ver only (TMK) in that it has a two piece crankcase and bolt on rather than bolt through muffler attachment. Oh, and it has the old ST muffler design, which although noisier, also offers it a power edge and weight advantage over the contempory design. Surprisingly, I haven't had any problems with this particular ST. It runs like a Swiss watch. I say surprisingly, because it's the exception to the ST norm IME. Don't know whether it's this particular random engine sample, or ST's .61's in general, as ST has fitted a MAG carb with sensibly sized venturi to this .61....plus a barrel which doesn't stick and transition slot which works.....for a surprising and inarguably pleasant change.