Land Rover Defenders have large towing capacities. UKTow.com lists the towing capacity of a Defender 110 as 7700 pounds and a Defender 90 also at 7700 pounds despite the shorter wheelbase and lower vehicle weight. According to UKTow, in the UK, towing capacity is determined as the weight of trailer that the vehicle can move, from a standing start, up a 12% grade.
For importation, check out this link… http://www.nhtsa.gov/cars/rules/import/elig092210.pdf
The "25 years or older" rules are not universal. Basically, imports older than 25 years do not have to comply with the Federal Motor Vehicle Safety Standards (FMVSS), but imports newer than 25 years do. Some limited model years of the Land Rover Defender can be brought into compliance by a registered importer for sale in the US. But note, the newer model years only apply to the left-hand-drive Defenders. Right-hand-drive defenders still have to be more than 25 year old, no exceptions.
For Land Rovers, the document at the link above identifies which newer model years are also eligible for importation; but the selection is very
limited— only 1993 for the Defender 110, only 1994-1995 and the first 9 months of 1997 for the Defender 90. But as long as you deal through a registered importer, you don't have to worry about that; that's the importer's job to make sure he imports only the right model years.