The 1991 Allez Epic Ultegra had an MSRP of $1,355 and the Allez Epic Dura Ace $2,169 according to the 1991 Bicycling magazine buyer's guide issue. The 105 SC equipped bike for 1991 was the Allez Transition at $922 but it was not carbon... Direct Drive CroMo whatever that is.
Perhaps someone swapped groups on your bike? Looks like '91 would be 600 Ultegra or Dura Ace only.