In order to remove a front sight base that is installed with taper pins you need to support the sight base on a piece of hardwood with the ejection side down. The taper pins come out left to right and are installed right to left. Break the pins free using a 1/4" diameter drift punch with a good sharp blow. A series of light hits may peen the ends over like a rivet. An 1/8" drift punch tends to skitter off the pins so you can not get a solid hit with it. After the pins are broken free they can be drifted out with the 1/8" drift punch. Tap the sight base off the barrel with a plastic mallet.
Front sight bases and barrels that have the sight bases installed with taper pins are not interchangeable. Once the sight base has been installed with taper pins it is unique to that barrel.
To reinstall the sight base install it onto the barrel and line up the holes as close as you can by eye. Insert the taper pins from the right side as far as you can by hand so the sight base will mount to the same position on the barrel. The pins are then set with a hammer.