In 1948 the 8 cylinder engine and hydramatic transmission were such a popular combination that some cars that were slated to have the automatic with a six cylinder were changed on the assembly line. There’s a somewhat crude secondary plate under the main one indicating that. The Pontiac club ran an interesting article about it a few years back.
In case you’ve not found it yet, the imperial club has owners manuals, service bulletins, etc. for your car available free for viewing: https://www.web.imperialclub.info/Yr/1939/index.htm
@Hemi Joel in case you’re still looking…
You migh check this (May / May not be usable) online auction out of Winnemucca, NV https://beta.govdeals.com/asset/147/21935
there’s also an old post here, in case you didn’t see / follow up (does not state sold):
Anyone making a purchase would want to clarify ownership, as the ad states “I bought it for my ==> ex <== back in 97, it was in his name and he passed away.”