TORQUE SETTINGS----Head-190 inch pounds   Cylinder-210 inch pounds
Compress the piston ring with your fingers and slide the barrel over the piston. DO NOT FORCE ANYTHING at this stage. BE GENTLE. Quality women and engines like gentle. Once the barrel is seated, turn the magneto rotor and rotate the engine. The piston should slide up and down easily. Do not forget to place the clutch flange back on the engine BEFORE tightening the barrel nuts. Tighten the barrel to 210 inch pounds, bringing it up to tightness in 50 inch pound increments.
Install the head gasket with the UP marking pointed UP. Don't be a dumbass tightwad and try to reuse the gasket. The thing is stupid expensive, but a blown headgasket on your second practice lap is more expensive. Install the head onto the barrel and tighten the bolts to 190 inch pounds, bringing them up to tightness in 50 pound increments. Install the hoses and carbs and you are done.
Once you have your motor back in the kart, you should take the time to break in the engine correctly. Here is my recommendation.
FUEL-use your regular race fuel
ON STAND RUNNING-3000 rpm for 5 minutes.
ON TRACK-One five minute segment with no greater than 11,000 rpm. Allow the motor to cool down. Another five minute segment with not greater than 12,000 rpm. Cool down. Go race.