I have a 73" sbach and the 35 should be ok. Mine has 5.2" from firewall to prop hub (using a Syssa 30 on a Pilot-RC Sbach 342 with the carbon fiber parts). I used an ignition battery eliminating circuit (with the opto kill) to save a few ounces but ended up having to add the weight back to balance. More engine would be nice instead of the dead weight although the Syssa flies it exceedingly well with NO lack of power. I agree with Jimini about the plane being designed for a 30cc engine being capable of taking a 35cc engine. Just compare prop and rpm data and "pick your poison"!