that thing looks like a thrust reverser... but there's something wrong with those engines as they have clamshell door mounts too
Okay, those ones on the sides of the engines are speed brakes. I realized that they would probably rip in flight, so I have reversed them. But for some reason, I seem to recall seeing that sort on some aircraft a while back. It may be just my imagination, but anyways . . .
And it does have clamshell reversers, which I modeled after the stock MD-80. Since the Gmax source file for the aircraft came with my copy of Gmax (along with the Twin Otter and a Piper) I decided I could really learn from it. Simply merged the engines into my files and then modeled alongside them. Really helped.