RE: Engine choices??
Dauntae,
From the reputation of these two engines... The .61 Webra #1024 is a high RPM engine, running with the best of its day (10 cc late ''70s-beginning ''80s F3A pattern engines). This engine should spin the 11x7 at ~14,500 RPM.
The .55 is a bored and stroked .40 frame engine, that is more in its element with a 12.25x3.75W. It is designed more for mid RPM torque, although a suitable exhaust (JettStream/UltraThrust) can carry it into higher RPM numbers, with a suitably small prop.
The Webra puts out more HP and should give the pretty draggy Bobcat significantly better speed.
I believe the Webra may also be pretty light.