I believe what the seller is saying is that he had a 400 engine professionally built by Nunzi using RA III parts for $9500 that puts out 425 hp (also the suspension and tranny from Nunzi). I don't see anything where he is claiming that's an OEM setup. More punctuation in the description would have been very helpful. If I had a lot of time on my hands I would go back through my Hemmings Muscle Machines and find his article.