I know you are thinking that's it's been a long while since you have seen an 1966 GMC pickup on the NASCAR circuit, but ROSS Racing Pistons also makes custom pistons for other engines. My goal was to increase the compression ratio for my 401M to 9.5 to 1 from 7.5 to 1. Ross was able to get the pistons to increase the compression ration to 9.0 to 1 by creating a flat topped piston for me. They also reduced just about one pound of weight from each of the new pistons. They weigh in at 3.27 lbs each!