A visit to Mike's Decals' "donor kit" listing on his website may be productive. They're usually bagged without instructions or Decals for decent prices.
I have 2 rear bench seats; 1 from the Revell 69 Nova and 1 from the old AMT Nova. If you want them, PM me your address and I'll get them into the mail to you. I don't need anything for them, just glad I can help!
I just did a Google search for 1936 Packard 12, there were numerous sites. I chose the one for Volo Museum and dozens of photos came up, including the imterior
Other than the decals, they basically already do. Salvinos JR has the NASCAR Camaro and Jim Rogers (the "JR" in Salvinos JR) offers the 3D printed parts for the conversion by email