As a general principal based on my experience, in matters where possession is an element of the offense, existence in unallocated is NOT sufficient to support a possession charge. This is generally because if you download something that you don't want and delete it, you are specifically not wanting to possess the item, and the remnant in unallocated is not your fault. The same principal also applies to files in your cache in many places, unless they have a specific offense for access, rather than possession.
All evidence is potentially good evidence and I would not rule anything out so broadly. A deleted link file is very good evidence.
Also be awareof your jurisdiction. The leading case on evidence in unallocated in the UK is Porter, which IIRC essentially says that you are not guility of possesion if you have deleted the images and have put them beyond reach, if you have deleted them and have a copy of Norton/encase/winhex/RevEnge then you have the skills to get them back and you may be judged to be in possession