To replace the standard stock with a Tapco T-6 (good choice, by the way), remove the trigger group and magazine, then take the receiver/barrel assembly out of the old stock. There is a trick to installing the T6 with the pistol grip attached. Removing the gas tube cover can be and often is difficult. To replace it, you will need to disassemble the BC group, pistons, and gas tube/handguard.
To replace the original stock, you will need the necessary 922 compliance parts. The oprod is not considered as it used to be in the equation. If replaced it counts neither for or against the magic number of 10 foreign parts. Good news: US made a hammer, shear, and trigger is being offered by Murray's guns over at sksboards.com. Also, Tapco will be releasing their US made bolt soon.
buckmeister