You don't need to machine the casings unless you go bigger than 103mm, I did machine my casing, I was among the first in the world to build a big bore 660.
I have just about done or been involved in every engine mod on these motors, if you want torque = big bore or bigger bore + stroker crank & standard cam, if you want to move the power up in the rev range the add a high lift cam, the more HP you want you will need to extend the rev limiter in the ECU. The more power put through the motor the clutch will need upgrading.
https://www.xt660.com/showpost.php?p=51632&postcount=59
https://www.xt660.com/showthread.php?t=5895
https://www.xt660.com/showthread.php...ighlight=xt700
Some bits if you want to go big:
CAMSHAFT:HOTCAMS STAGE3 FOR RAPTOR700 or Raptor 5050 cam
VALVES AND SPRINGS:BLACK DIAMOND+2MM RAPTOR7
CYLINDER:105,5MM FOR RAPTOR700
PISTON:JE 105,5 12.5:1 FOR RAPTOR
CRANKSHAFT:HOTRODS +5MM FOR RAPTOR700 CYLINDER TO HEAD STUD KIT FOR RAPTOR 700
FLYWHEEL STARTER CLUTCH GEAR FOR RAPTOR700
STATOR ENGINE MOTOR COIL FOR RAPTOR700
YAMAHA RAPTOR 700 CAM CHAIN
Dynatek Ignition Coil Kit Yamaha FOR Raptor 700
CLUTCH BASKET raptor 700 extra clutch plate
FLYWHEEL IS FROM RAPTOR BUT FLYWHEEL GEAR FROM XT660 ITS HALF.