First, our opinions don't matter, your friend should only be convinced by facts.
Second, the only factual statement that can be made to compare a solid axle to IFS is that they are different and each has its benefits and negative aspects. People in the "rock crawling" community generally agree that solid axles are better, but IFS is certainly the way to go for highway and baja.
Third, I don't know the exact dates, but it is fairly common for a model year vehicle to be manufactured in the previous calander year. As an example, there were 2007 Mazda SPEED 3 cars sold as early as November 2006. I'm sure it is possible to verify the correct year based on the VIN number, call a Toyota service department. Also, wouldn't the registration say what year the truck is?
I would agree that the IFS is a clue to it being a 1986 rather than a 1985, but it should be fairly easy to verify.
