Honestly it still looks very Necron to me...
A Big Mek would be a bit more Orky in Looting of this Monolith
How Orks loot vehicles...
1. See something you like.
2. Kill it.
They have to put it out of action to loot it first that leaves a lot of battle damage.
3. Fix it
the Big Mek needs to get it working again. All the Necron turrets, Grav technologies, the technologies needed to power the thing ect.
Everything that has most probably been put out of action need to be fixed. In a suitably Orky fashion of course.
Bottom like It is not going to look like a pristine version of the Monolith after they finish getting it back into action.
It will be bolstered up with whatever they can find to fix it. Scrap metal bolted on to cover battle damage not all battle damage (only the stuff that really needs to be covered, Orks are lazy after all), Boostas or tracks to replace the Grav tech ect.
4. Add Dakka.
The more Dakka the louder the noise. The louder the noise the better.
Just add heaps of Orky guns everywhere.
Also, grabbing claws, whirling blades, buzz saws, deff rollas and the like.
Basically make it look like a killing machine.
5. Make it your own.
Ork slogans and Glyphs, grots everywhere, Waaagh banners, a new lick of paint (preferably red to make it go fasta)... the list goes on.
Also removing any markings that it's previous owners had is a must. It has new owners now and they'd like everyone to know it!
6. KILL SOME THINGS, BLOW UP STUFF, DRAG RACE SOME SPEED FREAKS...ECT
So, while you have done some of this. There is still a lot more you can do to make it look a lot more Orky!
A few Images for Inspiration perhaps?
Hope this helps!