I tell them it is a well-built replica (which is the truth) and that it is well enough done that it has fooled a number of very knowledgable people (which is also the truth..l had my head in the trunk of my replica and someone came up to me and said they had not seen an original on the street since they worked on them at an auto dealership back in the 1960's). I then tell them that it is likely that it could outperform the originals and that it is no more expensive than a decent new mid-size car. That's usually TMI..."yes" or "no" would probably have been enough.
Cheers!
Dugly