This is a clone wars item I believe (so does the seller) but neither of us have a clue as to what, and its now in bits. Doulbe cannon at front (pivot sideways) 2 engines, not an AT. Side fins beside blasters are marked as 501st.
Searching Bricklink for pieces that have "501" on them results in a delightfully short list, of which two possible items emerge:
The second one can clearly be seen in the first and third assemblies, and the palette of the pieces in the second assembly is strikingly similar to this one, so I'm quite sure it's a MOC of that one.