You can replace the M. S. H. By just changing it out with a new housing But all the parts are not the same. The spring in the I L S housing is shorter and the cap on top of the spring is different, longer I think.
The mainspring housing pin retainer may be the same. You will also need a
mainspring cap pin.
If I were to do this I would get a new housing and all the internal parts to go with it. The housing is the expensive part the internals are not.
That way you can keep your I.L.S. one complete.
My 1911-A1 loaded has a 28# mainspring this is common in Springers.
Also a Titanium firing pin and a very heavy firing pin spring.
The firing pins are not standard I believe they are 38 supper. Ed Brown has them in steel and I thing they come with a heavy duty firing pin spring.
The parts are set up to work together. I have read many post that say they changed the housing and left the firing pin and it's spring as it was.
If you change the M.S.H. and go to a lighter main spring like a standard 23#
You may--I say may get light primer hits with the old firing pin and it's spring.
I hope this helps.
Shouldn't oughta point a gun at me if your not going to shoot.--------It's insincere.