RON L here = SERESURPLUS
Removal of this part, is really no real chore! First and foremost, Clear the weapon of Mag and check the chamber! Lewt the Hammer down the set it on the bench! Get yourself a small Wooden or leather haead covered mattel and a Brass Punch of the correct size to for the pin in that part? Go from Right to left and tap the Pin out of that hole, the Hammer Strut will push the Mainspring Housing out if it's loose enough, or you may have to help it slide down off the lower reciever! It (Mainspring Housing") will then slide off as a unit, this little bugger has the Housing, the Spring, the Cap and a pic holding it all together, Be sure not to let it get dirt and grit in it, does your new one have all the components or are you gonna remove from the old one? If so, you will see a PIN in the Housing Holding Down the TOP Cap, tap that Pin out and that will allow the Pin cap, spring and all to pop up up, (SOMETIMES QUITE FAST)! Try to Hold that Down as you tap the pin, yes it takes 3 hands sometimes? That should allow you to see the other off assembly and you can simply remove from the old one and insert in your new one?
Hope this Helps, if not, ask and I'll try to help more>? I do have CD ROMS with the complete break down of the 45 1911 as well as others, if your interested? If not, so be it and ask if we can be of any other help?