I have come across this a few times when checking databases for which oil filter and air filter to go with. Usually, the databases list two engine options, the Disco II V8 4.0L and the Disco II V8 4.0L (3950) 2. For example, the E3 spark plug listing:



Is the "(3950) 2" a California specific model?

 

"2" is the VIN code for the engine. I guess some 01-02 models used a different engine. Is that when the Bosch engine management was introduced? That would make a difference. Guessing the "2" is the GEMS motors but don't know for sure

 

All D2's are Bosch management systems, the 99, 00, 01 and 02 were 4.0 engines, the 03 and 04 are a 4.6.
For the most parts they all take the same filter and plugs, as an example; K&N 3001 and Mobil1-301 oil filters fit all. The Bosch Platinum Plus 4 plugs works in all of them.

 

ALL Disco's have the same enigne, the 4.0 is the 4.0, DI or DII does not matter. The only difference between the engines is the engine manegment. DI's have the GEMS and DII's have the BOSCH.
The 4.6 is a stroked 4.0.
The different numbers that you are seeing is for the emmisions, so do you have secondary air?
The spark plug temp will be the difference between the two plugs.
You can double check your VIN# or do a cross reference to find out for sure, but you will be fine with either plug number no matter if you have secondary air or not.
They are the same length.