Oh wow, nice minigun there. My miniguns were rather rushed, I spent more time looking for a certain part (which I eventually ended up just switching out the hinge I have for the windsheild for it) than I did actually working on the gun. I was going to make a Particle Cannon or a large flamethrower, but I decided to keep my symmetry and go with my miniguns.
My pictures do the elongated head no justice. And while I have plenty of roosterpit windows, including a black version of the one you used for the Jackal, I decided to use the Imperial Fighter windshield because I love the bubble-style roosterpit idea, it gives it a more futuristic theme.
I'll definitely make more mechs, this was so much fun and kept me occupied for a long time. But first I need to order some pieces I ran out of, like those little hinge-ish pieces. You can clearly see what I'm talking about if you look at where the minigun arms are attached to the base. I also used one to attach his chair to the rest of the roosterpit. I also have two of them attaching the side panels to the main turret piece.
I use
http://findmybrick.com I find they have all the pieces I need and good minifig parts.
Also check out
http://brickarms.com for modern warfare weapons.