Hi Jim,
Short answer: SAITO 125 - no way; 30 cc gasser yes! Long answer: current pattern set-ups have a thrust to weight ratio of around 2.4 to 2.6 to 1. You don't need that much power, but I would recommend a thrust to weight ratio of at least 1.5 to 1. I don't know much about gas engines other than the OS 33GT, but if you can get at least 7,000 rpm on a 19x8 or 20x6 prop you will have good aerobatic performance capability. An underpowered pattern ship is really not much fun to fly.
I have a 78" Extreme Flight Extra which is pretty much current pattern plane size. It weighs about 12 pounds and is powered by a piped OS 1.60 turning an APC 19x8 at around 8300-8400 rpm which is slightly more than a 2:1 thrust to weight ratio and it flies like a pattern plane. I am assuming your gas engine would just be muffled and your Element really shouldn't end up weighing much more than 11 pounds.
Good Luck,
Will