My bad, the aircraft in question is a Byron kit Ryan ST-A, 90"ws 66"long, about 18lbs.
I at first was going to put a Ryobi 31cc in it but now it appears the 46cc Poula is better and cheaper, OTOH what I do have and willing to convert is what I think is a 60cc MAC 610 chainsaw, the number on the Walbro is #21-245-2 can this identify it better? Only other thing is to see if it is a viable fit, the cowl is long and roomy though.