LR4tq, Overfinch has been offering upgrades to the US owners for decades. They make body kits, handle performance tuning and can do custom interior work. For awhile Overfinch was the only company offering third row seating kits for Full size Rovers. They are in no way connected with JLR or LRNA. They are just another tuning and customization company. They are very popular with the full bodied owners as they tend to a bit more reserved in styling than some of the more drastic, wide bodied and in your face body kits on the market.
In addition to customizing for individual owners they also purchase cars to to show case new designs and show off their work. Then retail these on when they are finished in the advertising and car show circuit. The demand was so great in the US they finally opened full facilities in Virginia about the time the L320 was introducted here. This was followed by Richmond, BC for Canadian and NW US customers.
As far as this particular example I don't see performance upgrades listed in the advert, but the dealer may have no clue if there has been.