I'll try to give the whole story (that I know to date). I bought the 4 Runner from the original owner ( I have the original bill of sale and window sticker!) in Orange County (So Cal). The original owner bought it in 1985 in Seattle and moved to So Cal two years later. It is a "base" model, 22RE. He was told at the dealer that the "base" model was imported w/o the back seat to save $ on import fees. The vehicle was considered a truck for import.
My guess is that a shop in So Cal took delivery of the 4 Runners from Long Beach, added the back seat using Toyota supplied fabric, but using their own brackets etc. They then affixed the "RVIA" badge on the tailgate ( I'll post a picture) and returned them to Toyota to ship to dealers.
The local Toyota dealer's info I think confirms this. They ran the VIN in the computer, and it showed no back seat. There were back seat parts and info for SR5s. On a hunch, I ordered the striker and latch for the SR5, but it doesn't fit.
I don't think it is a "treckker" because it is an 85. And finally, with the exception of the back seat, everything else is 1 generation 4 Runner and listed in the Toyota parts computer.