I have a blue label Colt 6520 with 2 position collapsible stock. How difficult would it be to drill a couple more holes to make it a 4 position? OR would it be more beneficial to purchase a new Colt 4 position with H buffer. Any input would be helpful.Thanks.

Do yourself a favor and do not modify an original Colt stock part. They tend to be spendy and at some point you may want to reconfigure your weapon back to its original configuration. (Makes it worth more)

There are lots of current manufactured Colt OEM parts, like a 4 position tube, that you can simply "bolt" on. Get one from WES at MSTN and he will get you all setup right.

I would strongly advise against altering your factory original 6520 collapsable stock receiver extension (ie tube).  Your rifle is worth a whole lot more more with this in original/unaltered condition, and you will regret it someday.  If you would like to have a 4 position c-stock, just purchase a new Colt collapsable stock set-up, and have it changed out by a competent individual.  Put the original away for safe keeping so you will have later when you want it.

Just my opinion, hope it helps.