The newer grips will fit an older model without any "fitting". The reverse is possible but a small notch needs to be worked into the older grip panels where the newer mainspring cup is. There was a recent thread on this with pics on the SiGForum and I meant to bookmark it but was at work. I'll look around for it an link it when I find it. Exteriors are the same so no problems there.
Welcome to the forum, btw.