Looks like you are doing quite a faithful reproduction.
It's kinda funny. I have a mint SPAS-12 folder and the forearm and barrel guard is the part I dislike the most other than the idiotic redundant safety. Also, every pump of the action rubs on it so it slowly grinds away the finish at the contact points.
Really, the SPAS-12 is an iconic shotgun, maybe simply because of its unique look, especially the folding stock with hook version. But, the Benelli M3 top folder is a MUCH better shotgun in every way in my opinion. The very rare (in the U.S) SPAS-15 fixes all the oddities of the SPAS-12 and gave it a detachable magazine.