That is a manual decocking lever. It is used on traditional double action firearms, mostly guns derived from the colt 1911, to manually drop the hammer safely from a single stage trigger pull to a "safe" dual stage trigger pull. On the first shot with a DA gun you hve to first pull back the hammer into the ready position, the second stage of the pull just drops the hammer on the firing pin. With follow up shots the slide primes the hammer so you only have to drop the hammer giving much lighter trigger pulls. Thus increasing accuracy.
Funny you should use the 1911 as inspiration. Designed by john browning in 1911 that gun saw service in both world wars, korea, and vietnam. Why not see service against alien invaders too. Today most military and police forces have moved on to better things (much debate among enthusiasts of course), and the 1911. The 1911 is mostly a show piece these days but there is also a thriving community of enthusiast shooters and modders because of its history. I learned to shoot combat pistols on the 1911 platform.
The best 1911's are made by ed brown and wilson combat if memory serves. If you really want to do the design justice look up some of those pieces. Might as well keep true to the design if we go that route. I don't see why the slide at the top shouldn't line up. There is also a weird pointy thing on the grip I don't understand.