Air pump advice
I have a 1991 300TE which just ate another air pump, and it's possible you have the same component. If you have a serpentine belt arrangement with the air pump driven by electric clutch, it's most likely the same part. I can get the p/n if needed.
It might be possible, if you're ambitious, to try to get an equivalent bearing that's close and machine it or the pulley housing to get it to fit. I thought about this and if you screw it up and decide to get the new pump, kiss the core charge goodbye. That and the fact that several dealers told me the pump side of this part usually dies around 150 k miles anyway.
Long story short, no one will sell you the pulley bearing by itself. The best I found was a good rebuild from Randy Steele for $350 w/$150 core. The R/R on the I-6 is a PITA because the injection hose is hard to get to without a lift. Also, check and see if you have a vacuum operated air injection valve in the line going into the engine. Mine was toast, replaced it with the new rebuild for $40 and I suspect that's what ate my first rebuild. The pump R/R itslef is only a few minutes without the hoses because it's only held on with two bolts.
Good luck, and feel free to post off-line if I can answer any more of your questions.