RE: Bigger engine for U-Can-Do .46?
What is your all up weight now?
If it is near the 6lb mark, a 55AX will be enough with a macs #6720 or #6724 one-piece muffler.
The stock muffler may leave you a little short of good pullout.
My personal choice for this would be a YS70. That will get it done and put a smile on your face.
In comparison the YS70 is a good 3 oz. lighter than the OSFS70 and has MUCH more power.