The hammer pin and sear pin have heads that go to the left, that way the manual safety keeps them in place. The mainspring housing pin has no head and can go in from either direction, but the round end goes in first. The mainspring cap pin has a head and goes in from the inside so the sear spring holds it in.
The only pin that requires any force to remove or reinstall is the MSH pin; it is retained by a plunger that is on the end of the mainspring and fits into the groove in the pin, keeping it in. The hammer and sear pins are easily removed with the fingers or any small round object, like a ball pen.