has anyone found any aftermarket heads?

 

http://www.engine-parts.com/GMV6/gmv6heads.html

try that, there are a ton of parts for 2.8/3.1 on that site.

 

Dave is also selling ported/polished heads with a three angle valve job here on the V6 board.

 

Those will just be stock reconditioned heads.

the only true aftermarket heads that I have seen for the 660 was from a company called Potter. I have not found a distributer for these heads however, or any more information on them.

What I have seen was these heads used on a mechanical injection idividual throttle body equipped, 2.5L (destroked), used in some form of hydroplane boat racing, making over 400 HP.