If I could build any replica, I would do a Ferrari 250 GTO. Actually, a friend of mine IS doing one, using a 330 America donor car and an aluminum Allemano replica body. It is quite close to the original. The project has stalled a bit ($$$$??) but is well along and driveable. Mostly I think it needs paint and trim to be completed.
The other car I really admire is the SWB Berlinetta. Several of these were duplicated a few years back and sold as originals (one British peer went to prison over it, actually), but they were quite well done. If you were building one as a replica, you could put in a bigger engine and the 5spd gearbox and really have a rocket.
As for the Miura, they are still available at a cost that makes doing a replica beside the point, but not for long. They are starting to go up. They are higher maintenance even than a Ferrari, according to my friends that own them, and break a lot. But they do go fast, sound great, and look GOOD. /ubbthreads/images/graemlins/grin.gif