If you are going to build a DRAG ONLY shee....
4 mil cub
4 mil crank
NOSS head with domes cut for methanol and blaster pistons, 20cc
10 over to 12 over swingarm
Override trans
Lockup clutch and cover
FAST Clutch
39mm carbs or bigger
Out of frame Shearer or CPI pipes (depends on what your builder suggests)
Longer Chain
Different gearing (depending on how long of distances you want to run)
Marvin Shaw rear shock
Once you're done with that....buy all the lightened hardware you can, axle, arms, etc.
Also...Methanol requirements for 300 foot vs. 1/8 mile is going to be different, could be the difference between running billet bowls, and billet bowls, a fuel pump, etc. So...how far are you going to run?
If this is going to be more of a duner than a drag bike, keep it on gas, but stay with 39mm or bigger carbs....but you said drag, drag racers use methanol.... It's cheap 5-10% more power.
Actually, you're in luck.
blewbyu (Jeff) is selling his 4 mil stock cylinder setup. It would cost you half as much to buy this setup, and with his 180lb ass on it, it kept up with our big 4 to 10 mil cubs all day long at the drag strip, it would be a FRACTION of the price....and you could spend money on light go fast parts, powder coat and chrome/billet accessories.
I will let him give you a run down on what he has, but he went with a bigger 10 mil cub motor, and he's already torn down his old motor and is ready to sell it.