The real challenge in putting a 4R55E into a 1st gen is the electronics. As I understand the 4R55E (sometimes called A4LDE) bolts in just fine in place of the A4LD. The problem is there isn't a 1st gen PCM that can control all the electronic features in the 4R55E, since the A4LD only had limited electronic control.
There's a stand alone controller for the 5R55E, so I expect (though I haven't yet heard of anyone do this specific swap) that putting a 5R55E in wouldn't be overly difficult. I haven't heard of a stand alone controller for the 4R55E yet, unless the 5R55E controller can also control the 4R55E.
A '94 and a '95 are pretty similar in terms of engine management - I wonder if you could use a '95 PCM to get the 4R55E to work in a '94??