I got a S&A MSH installed and I used the stock ILS spring, MSH pin and Mainspring Cap Pin. seeps to work fine but I've seen a couple threads saying they should be replaced with none ILS parts. is this true?

Yes, the hammer strut bearing cup on the ILS plunger is longer than a standard one(the ILS has .165ish longer side walls over a standard plunger), and this prevents the hammer from fully returning all the way forward at the uncocked position ( the ILS MSH unit does not use the lock pin, and allows the plunger to ride higher in the MSH that the retained plunger).  

If needed, you can either use a stock plunger, or just take .165 off the plunger strut cup retension side walls to allow the bottom of the plunger cup to sit in the correct unoaded position when locked into the MSH by the cross pin ( the bottom of the cup where the hammer strut rides).

P.S. Email me and I can bounce back a photo of the ILS and a standard plunger together so you can get a better understanding if you just want to chop the ILS skirt down.

well I'd just buy a new part, since it's cheap and i'd like to keep the original parts incase i go back to the stock look for any reason. thanks for the reply though

Did the same as you several; weeks ago.

Replaced the GI .45 ILS-MSH with a S&A checkered MSH, Colt MSH Pin, Colt Mainspring Top Cap and Colt Spring Base. But when I tried swapping a Colt Mainspring, it looked way too long. I knew if I compressed it so much to fit in the housing, it would be waaay stiffer than the original Springer Main Spring. So I just loaded up the Original Mainspring in the new MSH with the approproate Colt top and bottom caps. Slide in the new MSH retaining pin and fitted back to the pistol.

Works fine, trigger feels a little smoother without the ILS unit, will be having my 'Smith replace the extractor, ejector, and probably put in a Wolfe Sear Spring at the same time.