this is now VERY old, one of my first models from years ago, at the moment im workin on some vostroyans, and i have some kasrkin and skaven to upload as soon as i get time, of decent quality (i.e. they dont look like they were done by a 5 year old)
first, get rid of the distracting background, take the picture on a white t-shirt if need be.
second you NEED to make this more orky. I would paint the whole tank in ork colors, lots of red.
I dont know if the orks would use all the imperial accessories, i think they would rip them off. Add ork bits in there place. You can leave places where the tools would have been.
paint the inside of the gun barrel.
drill holes in the heavy bolters. (10 dollar pin vice from radioshack)
There is a lot more, but im tired, you should check out ork forums, like....
http://www.the-waaagh.com/home.htm
Good stuff, lots of ideas, ask them for help.