I have a Colt pre-ban "Govn't Carbine" with an A4 upper receiver.  It's a very cool (my favorite) gun.  But I would like to modify the lower receiver so that it can take post-ban uppers like Bushmaster, DPMS, etc.  The Bushmasters have the "forward" pin just like the rear pin... push out the rear pin and the upper pivots away from the lower.  Pust out the "forward" pin and the upper and lower come apart.

My Colt has the "small" screw at the foward position, and has a small hole on the right side of the lower receiver.  This, I think, makes it easy to convert the lower to accept the uppers with two push-pins.

How do I make the modification?  What parts do I need?  Any more info you guys/gals can give me would be greatly appreciated.

Thanks for your help.