RE: Shrike. Irvine 53 or 46fx?
I think the plane pictured is the ARF and that makes it a little hard to move the firewall.
You might try a wood prop and a tuned pipe or mousse can muffler. Both of these will move the CG back a little. I would also use a 1650 mil NiMH battery, put way back.
Also check to see if you can find a lighter front wheel.