Ok as for say a beavertail and commander hammer ya got to grind the frame for proper fit of beaver tail unless you go with kings drop in very nasty gaps though..
Ok for mainspring housing change..
If you have ILS cock hammer stick ils pin in hole on right side of frame.
Decock hammer then drive out pin at very bottom of grip.
Grab mainspring housing and pull down out it comes...
Then if your using a non ILS housing you need the housing mainspring cap and mainspring housing pin retainer,mainspring cap pin and a new mainspring .. the parts from ils wont work with a non ils housing...
Assemble housing slide up into frame push up while lining up the hammer strut with mainspring cap.. push up more since you have to overcome some spring pressure then push in retaining pin and bam your done