The -600 has the same rear fuselage as the A310 with the rear pressure bulkhead moved back a couple of frames. Therefore although the fuselage is only 46cms longer than the B4
, in fact the -600 has two more seat rows and carries two more LD
The A310 and -600 have the same "glass cockpit" and fly-by-wire secondary controls ie spoilers, airbrakes, lift dumpers, slats and flaps.
They also have a carbon fibre fin and rudder and a trim tank in the tail plane.
The A310 (only) wing is new and the tip fences are different to the -600.
The two-crew B4s were sold to Garuda, Tunis Air and the charter are of Finnair whose name I can't remember. About a dozen in total.