Long rod engine have a longer connecting rod but the engine stroke remains the same (same CC size).
The longer rod length will reduce the rod "angle" during cranking and this will help reduce cyclinder side wall stress (less cylinder wall friction, better pressure seal and more reliable)
I have not try long rod before and cannot tell the real difference it will made to the power. But if you get the long "stroke" engine will give you more torque instead.
The stock 26cc engine uses 34mm piston with 28mm stroke crank.
29cc engine uses 36mm piston with 28mm crank.
30.5cc engine uses 36mm piston with 30mm crank. (and hence more torque but less rpm due to longer stroke)
For the servo, the throttle servo is 6v analog only and you should change this one to digital. Savox 0235 or 0236.
The steering is already a digital (made by Savox) and can support 7.4V Lipo.