I would like to change out the mainspring housing in my Kimber 1911 to a metal one (Ed Brown). Is this something to get a smith for or is it something I can do? I have assembled/disassembled AR15's w/success.
With the hammer forward, you can punch out the retaining pin at the rear bottom of the grip frame. Housing slides down, out. Replace with the new one, taking care to keep flatspring in place and the hammer strut in the proper hole, slide on and replace pin.
With the experience you have had, you'll have no problem.
Some additional help.
Field strip the gun.
Wrap tape or a couple of rubber bands around the grip to hold the grip safety depressed.
This will prevent the sear spring from moving out of it's seat and will make the job MUCH easier.
Lower the hammer ALL THE WAY FORWARD to take the strain off the MSH retaining pin.
Push out the MSH retaining pin, and slide the housing off the frame.
Get a small finishing nail and drive it into a wood block until about 1" inch is sticking up.
Use a file to round off the head.
Put the MSH over the nail, so the mainspring cap is on the nail and press down HARD.
Holding the MSH down, use a small punch to push out the tiny pin on the top of the MSH from the OUTSIDE. (The inside of the pin is flared to hold it in place).
Ease up on the MSH and remove the mainspring cap, mainspring, and the MSH retaining pin retainer. (This is a cone-shaped plunger on the bottom of the spring. Sometimes the retainer stays in the MSH hole, get it out).
Install the parts in the new housing, and reverse the above to install the housing on the frame.
There is one more thing you need to consider if it's a Series II Kimber. The little tabs on top of the MSH determine how far back the grip safety sits. This determines if the Series II push rod is flush with the top of the frame. If you let the GS sit too far forward, the push rod will stick up above the frame and your slide will get stuck when the rod gets behind the FP stop plate.
You will need to file those tabs on the faces so the push rod is flush with the top of the frame. Take a look at the thickness of the Kimber plastic MSH tabs when you remove it and make sure the metal one's tabs has been filed down to the same thickness or so the push rod is flush. Put it into the gun to see.
Kimber on the left, S&W MSH on the right. See the difference?