17 digit vin numbers didn't start until around 1979 or 1980 for most car manufacturers I believe, so most Jaguar VIN decoders won't work on a 1974 model.

The BW in the VIN is for Borg Warner, indicating the type of transmission that came with the car. If you look at this link and scroll down, the table shows that UE2N is a 1974 XJ6 with the standard wheelbase as opposed to long wheelbase. The 53793 is the chassis/identification number of this particular car.

http://www.johnscars.com/xj.html

If you go look at the car again, the engine number is located on the engine block, right where it meets the transmission bellhousing, on the driver's (LHD) side of the engine. It may start with 7L. That number can provide some information when it comes to replacement parts and such.