Did you see the eBay auction that just ended? Bidding went up to $18,800 and didn't meet the seller's reserve! It had to be the most rare GMC engine I've ever heard about. Not just any old(!) 12-port aftermarket head, but the aluminum version that Howard Johansen developed. It made 355 dyno HP n/a on alcohol with 297 c.i.- back in 1952! Only 10-12 of these heads were made. The Howard head on the eBay engine (in Paola, KS) had also been "massaged" by legendary head porter Joe Mondello at some point in time.