Big truck 292 (C50 and C60) engines had the 2 1/2 " 3 bolt manifold. I have a few of them. 250's also had a 3 bolt version with a smaller output. Have to measure it but it is probably 2 1/4". Tom
Inliner Member 1716 65 Chevelle Wagon and 41 Hudson Pickup Information and parts www.12bolt.com
