As much as I like the Poulan chainsaw engines, they are a bit large for 1.20-size aerobats like the GSP 72" Katana you're thinking about. I'm sure it will fly it like a rocket and 3D like there's no tomorrow, but normal aerobatics will not do well. Heaven forbids you get a flameout near terra firma... it will drop like a rock.

The 46cc and 42cc are perfect for 25%- 27% aerobats, planes like the GP Wagstaff Extra, H9 80" Cap and Kangke Texas Hurricane. Problem with the smaller Poulans is that they use the exact same crankshaft as the 42cc, which is BEEFY. Even the lowly 33cc will end up weighing around 4lbs or so. No big deal on a 16lbs plane, but a little heavy for something that's suppose to be 10-12lbs RTF.

For 1.20 size aerobats, look at equivalent gassers to the G-26. I just got to run my two Kioritz 25.4cc (exact same displacement as G26) with SynchroSpark CH ignition. They both turned an 18x6 at around 7500rpm, and should get better as they break in some more. RTF weight is around 3lbs.

The new Ryobi 31cc and the Homie 30cc, both twin ring engines, might also be viable choices. The Homie needs a judicious trimming of excess metat. Done well and with electronic ignition,both conversions should come in at a little over 3lbs.

I also like the 30cc and 33.4cc Echo chainsaw engines, but I don't know how easy they convert, as they are not popular candidates for RC conversions. They sure do look lightweight, though.