The Passat B4 cluster is pretty much plugnplay with the early T4a models (93-96 in NA). However the U.S. B4 clusters are all fully electronic, whereas the T4a models use a cable drive for the speedo/odo. This makes the B4 cluster the Provence for engine conversions that require this electronic VSS like a TDI. Although the fanatical (ie adventurous) could certainly install an electronic VSS on their trans, ditch the antiquated cable and utilize the electronic B4 speedo/odo and have a cool lil sleeper mod.
The later T4b models (97-03 in NA) have a redesigned dash and utilize the next generation cluster, very similar to an A4 Jetta but the T4 one has different mounting tabs so A4 fitment into a T4 would require some custom work.
Fitting a B4 cluster into a later T4b would not be easily possible due to the redesign of the dash and inherent space limitations. Also cluster wiring would be a minor nightmare as the plugs are different and all 22-28 wires that go from the fuse block to the cluster are all the same color: white.
Justin
2000 EVW 5-spd TDI