Do the A330 and A340 share the same specifications?
 

Do the Airbus 330 and 340 share the same specifications except for the 2 additional engines on the latter?

well i know that one difference is the range

Which specifications do you mean?
Both aircraft are quite different, even if they have many things in common. Engines (as already mentioned), Langing-Gear, Fuel-Tanks, just to mention a few. And even the A340 comes in 4 different versions (-200, -300. -500, -600).

Common type certificate (the basis under which they are certificated)

Common crew qualification (lets 330 pilots fly 340s with minimal training)

Dissimilar specification (the thing airlines buy them against.) - I doubt that any two airlines actually have the same spec, even for outwardly the same aircraft by design - there are probably minor guarantee differences for everyone.

Having flown the 330-200 and 340-300, essentially yes. Taking into account the obvious Donkeys, Ctr gear etc.

The range is not dissimilar but the payload is. The 330 has the fuel capacity to fly as far it just can't carry much when it does.

If you go to buy an A330 or A340 Airbus will give you a "Standard Specfication" document that defines the baseline model of whatever you want. Other documents will list all the options available etc. These Standard Specification documents are customised for each model eg A330-300, A330-200, A340-200, A340-300, so from the point of view of defining exactly what you are buying they are all separate specification documents.
However, in design, engineering, construction and operational terms there is a great deal of commonality. With the original A330/340 models Airbus basically set out to build a long range 4 engined aircraft and a medium range twin utilising the same airframe (as much as possible), same tooling and assembly line, same cockpit, same systems and so on.