Along with being in the trucking business since 1964 and growing up in the gasoline business I was a licensed salvage dealer for many years. A book called the Hollander is what salvage dealers use to determine what interchanges and a lot of it is just remembering what worked last time you tried it. I will be 78 in a few weeks and there are not many of my generation left that still do things the old fashioned way. I think the 3. 90 and 3.38 fit in the same GM corporate housing. They call it a H033 at 3.90 and H0335 at 3.38. The 3.38 was offered behind automatics. The 3.08 was a Spicer which is a totally different animal. I still run a dozen trucks, have a couple of gas stations, but I dropped my salvage dealer's license a few years ago.

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