If Rick Deckard is a replicant, who was he originally modeled from and where does his unicorn memory come from?

Or it could be that Ridley Scott didn't have any footage lying around of sheep for his directors cut... but he DID have unicorns and electric unicorns are way cooler than electric sheep.

@AngusThermopyle  very cool! 

I could be wrong, but I think the now extinct Unicorn signifies that Deckard [and Rachael?] may have been a unique, never to be repeated Replicant model.

I've always thought that Deckard and Holden were very similar, they even sound alike. Holden appears to be human, but could they both be variants of a unique replicant model?

Given the similarities between Paull and Ford, it's interesting, and perhaps cunningly clever, that Ridley gave Morgan Paull the part of Dave Holden.

Ironic bit of trivia- Morgan Paull was once considered for the part of Han Solo, but his agent told him Star Wars would flop, needless to say, said agent was fired and Harrison Ford became a star! :)