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My 88 was a little different, it had a ball joint with no gaskets. My headers are the same. The Y pipe is 2-1/4" to 3".I think the donuts between the manifolds and the Y-pipe are 2 1/2". Beyond that, I'm not sure--the OEM exhaust on my '88 K1500 rusted out and was scrapped two decades ago. It's now 3" from the catalyst to the tailpipe.