I know that the one of the pipes on the 3.8 pump is smaller than the same pipe on the 4.2. I think maybe it’s the pickup tube? Anyhow I measured both of the ones on mine (a 3.8 engine) which is currently out. The pickup tube OD is 7/8" and the output pipe is 3/4. There is no adapter sleeve on either one.
So do I have an actual 3.8 pump, or is it a 4.2 pump and instead of using an adapter sleeve the whole inlet pipe was changed out? I should be able to remember this, I mean it was only installed 19 years ago…age related?