Very nice work, especially the grip safety/frame fit and the mainspring housing fit to the frame. A few questions:
1) Although you stated the base pistol is a Series '70, it looks like a pre-Series '70 to me, based on the rollmarks. Is the pistol a 1960's Commercial Colt? Very nice base pistol.
2) Was the magazine well beveled to aid reloads?
3) Is the front sight staked? It looks like it in the pictures, but I cannot tell.