Mine is the one from VQ if I am not mistaken, but AFAIK it is the same. MIne is something like 155 cm or so, just a touch over 1,5 metre anyway. Weighs in at about 2,6 kilo, mine, and it does very nice on an FS91 and a 14 x 6 prop. Strictly talking gasoline conversion, of course, on MEthanol a .70 fourstroke would be enough and an 80 would already start to get ridiculous.
But with gasoline conversions, it's the old adage of "nothing substitutes cubic inches", and the 91 is the way to go.

Don't worry, it will most definitely fly with the 61, even on gasoline. Just not very powerful...