If I dont have the stock flywheel to match with my new flywheel how can I find out How many grams to add or remove so its balanced to stock lt1.

 

You have to rely on the flywheel having been manufactured properly, that's part of the problem with externally balanced motors. Many times with cheaper flywheels the amount of weight will be correct, but it will not be clocked correctly in relation to the crank. The only way to test is to have it spun up on the back of a crank and directly compared to the old, or a known good flywheel.