I wouldnt worry about the firing pin, I have never heard of one breaking. I replaced my Mil Spec with this Mainspring Housing http://www.midwayusa.com/viewProduct...tnumber=127124
which includes everything you need, and should drop in with no fitting.
"No man for any considerable period can wear one face to himself and another to the multitude, without finally getting bewildered as to which may be the true." Nathaniel Hawthorne