apparently the Saito 72 is lighter than the YS 63 and has got 10% more power than an irvine 53, but it should have better static thrust swinging a 13x6W instead of a 12.75 x 3.75.
Also Paul from Justengines says they will run on 5-10% nitro as well! Thats a bit better and cheaper than YS!
The fourstroke would work better with that smoke system your talking about by the way Phil.........