They make a jig that will hold the lower in place for you and will give you guide holes to run your drill press.
The problem(s) are
1. The tight tolerance for an AR.
2. Regular drill bits do not make a round hole. you will need to ream
3. Aluminum being so soft can show tooling marks very easy even from being clamped to tight.
I have a paperweight of my own. I would suggest just buying a 100%. Even here in Kalifornia they are only 130 bucks minus fire control group and hardware set.
"Any society that would give up a little liberty to gain a little security will deserve neither and lose both. "" - Benjamin Franklin