Standard GI extended beavertail

[parabellum]

First off, I don't own a 1911 or have any experience with them other than firing them with friends and family. I'm more of a Tupperware guy myself but I think one is in my future very soon. I have a limited knowledge of the gun in general, but need some advice from our long time 1911 guys. My father picked up a full size rock island armory GI for around 400 bucks. He wants to add an extended beavertail and replace the standard grip safety/beavertail.

My question is, which should he go with, and how difficult is it to do? Any suggestions or advice is appreciated as I will be the one handling the modifications.

Thanks!

Mitchell