I don't know if there are any production numbers around. GM destroyed most of their old records. They were two 351 V6 engines cast into a common block which made them twice as heavy as a V6 and twice as long and used twice as much gas. They were designed for class 8 trucks when Diesel power had already come of age. There are some around and I have seen several of them sitting on trailers at ATHS conventions that really did nothing than make a lot of noise. Their weight and size makes their application rather limited. They were rated at 275 HP and 630 torque.