Perchance have you read DinoJake's "The Last Spartan" (link here in case you haven't www.fanfiction.net/s/5939286/1… )? It's essentially a Halo/Mass Effect crossover where Spartan John-117 ends up playing the role of Commander Shephard, and he's given a "modernized" version of his Mjolnir armor integrated with Mass Effect tech. This sounds exactly like the description given.
to the fanfic, oh dude I am like writing two oneshots on haloxmass effect crossover and to tell you the truth I have no Idea where I'll go after the first chapters and I am tempted to write another one too.
I wish it was the original Bungie version; I really dislike the 343 version. It's lore-breaking and unnecessary. But, the idea here is cool. I'm sure the Chief and Shepard would get on good. Funny thing though is that Shepard actually outranks the Chief.