Ford actually designed and built DOHC small blocks in the 60's. 255ci aluminum blocks which put about 425hp and ran at 9000 rpm's. They won the Indy 500 in 65, 66, 67 and 69-71.
http://www.quadcamford.com/photogallery.html
Very interesting site. Ford sold around 20 of these engines I think for $20,000.
which is around $150,000. in today's money.
John O