Some time ago, another member purchased a pivot pin with integral detent to replace the screw on his Colt. He complained that the pin was a little too long and tended to slide back and forth in the hole.
I have no personal experience with this. Admittedly, it doesn’t sound like a big problem.
If you have a slab side (no magazine fence), this is your only option for replacing the screw. To the best of my knowledge, all pre-ban “AR-15” marked rifles are slab sides.
If you have a magazine fence, it is possible for a good machinist to drill a lengthwise hole in the fence for the traditional pivot pin spring and detent. This should allow you to use the tradition front pivot pin [b]if[/b] you have a small pivot pin hole.
This should give you an identical set-up to an M-16 (other than pre-A1 versions), and to most, if not all, non-Colt AR copies.
However, if you have a large pivot pin hole, you would need a large pivot pin. I don’t know if such an animal is available. (Note that I am NOT referring to a large pivot pin with integral detent, but rather a large pivot pin that will properly mate up with an external detent!)
Since Colt tends to use whatever parts they’ve got lying around when they make AR’s, it’s not totally inconceivable that your magazine fence (if you’ve got one) might already have the spring and detent hole already drilled in it - very doubtful, though.
Frankly, unless somebody really knows what they are doing, augering on a pre-ban lower is a very bad idea.