Range Officer parts

Anybody got a specific parts list to change the Range Officer MSH to normal 1911 for BM/Nelson conversion use?  What weight mainspring?  Differeint than for 45 use?  I think a complete MSH would be better to ease switching back to RO45 top. Specific part numbers for that too.  Also the sear spring needs replaced.  I hope to land right at 3.5# trigger.  Right now it is 4.5#

I already have a KC trigger kit installed.

Jack, I normally use an 18# main spring.  Yes a complete main spring housing with the new parts would be the easiest.  I use Colt sear springs.  Wolff gunsprings for the main spring or Brownells.  Brownells should have the rest of the parts for the housing as well.

Here's the minimum of what you need: http://www.brownells.com/handgun-parts/frame-parts/mainspring-parts/mainspring-caps/1911-auto-factory-plus-mainspring-caps-prod41836.aspx
You will need 1 mainspring cap, and 1 mainspring cap pin as well as the mainsprings you choose:
http://www.brownells.com/handgun-parts/frame-parts/mainspring-parts/mainsprings/1911-auto-mainspring-prod26265.aspx
My testing was done with the ISMI springs and 19lb mainsprings are a good balance for function and reliable ignition for a conversion.
If you are shooting .45 wad and iron sights with the same gun, you really need a strong recoil spring--I use a 19lb recoil and anything hot is really banging things up.  The recoil spring works in concert with the mainspring to slow the slide down during recoil.  Make sure you protect your gun by using the correct combination.

To build a complete mainspring housing:
http://www.brownells.com/handgun-parts/frame-parts/mainspring-parts/mainspring-refill-kits/1911-auto-mainspring-housing-rebuild-kit-prod27082.aspx
and pair that kit with whatever mainspring housing you like.  That kit comes with a 23lb mainspring so you could use that for hardball. 

Mainspring housings are all pretty good and a matter of preference.
I like the checkering on these: http://www.brownells.com/handgun-parts/frame-parts/mainspring-parts/mainspring-housings/1911-auto-mainspring-housings-prod24562.aspx
I have also bought lots of 1911 parts from ebay that included mainspring housings and got the whole lot for <$20.

As far as your sear spring is concerned, I prefer Wolffs but they are out of stock right now.  This one will work:
http://www.brownells.com/handgun-parts/trigger-group-parts/sear-parts/sear-springs/1911-auto-wilson-combat-bullet-proof-sear-spring-prod16460.aspx

Also, every time you change the mainspring weight, the trigger pull weight will change.  It will be heavier when you have a heavier mainspring in and lighter with the softer mainspring, so I recommend for a gun that's getting used for both .45 and .22 to go with the 19lb mainspring and a 19+lb recoil spring tuned for YOUR ammo.