FJ40s didn't come with a "window VIN" as on modern cars on the dashtop at the lower left side of the windshield.
There is a frame number stamped on the outside of the right side frame in front of the front tire, example: FJ40~123456.
This number should match that on the metal plate which is either riveted to the firewall, or attached to the inner right fender.
These numbers should then match the numbers on the legal paperwork(title) for the vehicle.
If things are missing or don't match-up, then something is fishy about the vehicle, and you need to be very careful you are not buying a stolen vehicle, etc..
I think your worry would be if/when you go to sell the vehicle in the future. Say you get it titled and tagged for yourself. You are happy and if your title shows 'No Liens' then that is good, hopefully no debts against the truck. But when you go to sell the truck the next buyer is going to do the same stuff you are doing, compare the numbers from the title against the tags or frame stamps. Might nix a sale, might not.
A little story...I bought a 1973 early Ford Bronco about seven years ago. Been working on it off and on, ending up replacing just about every piece of the body. Anyway, I am getting close to paint. I was thinking "Did I ever transfer that title to my name?". Go get the title out of the safe deposit box. Whew, yep, title is in my name. But then I notice the VIN. I was more keen on them since recently I was researching paint colors and VIN numbers. ALL early Broncos with a V8 begin with U15Gxxxxx (G meaning 302 V8). Staring at my title I see J156xxxxxxx. I am like WTF? I had missed that in buying the truck. Anyway, go to DMV. Loser behind the desk says he can't help me fix this, see the supervisor. Supervisor says they have never seen a VIN begin with U. I have the VIN plate in my hand, that I removed from the panel so I could bring it in. And I have VIN documentation from the internet. I get this long story about having to send copies of my title and everything in to title search, have some officer come inspect my vehicle to make sure it was not stolen.
I leave that DMV branch pissed. Wife says "Drive to the main office. Maybe someone there can help". I go there. Same story from the desk jockey. See the Supervisor. But this supervisor seemed to actually care. I explained I am restoring this old truck and it appears that when titled the U and the G were mistakenly put down as a J and a 6. All other numbers on VIN plate and title match up. Looking at the VIN tag, the stamp was hard to read the letters and one could think the J a U and the G a 6. So the supervisor disappears and comes back ten minutes later carrying a new title, with the correct VIN! I was very happy. They explained that when they pulled up my title, it was actually so old it was disabled in their system. And when he enabled it, it let him correct the VIN. They didn't even charge me a fee. So now if I go to sell, title and VIN plate match. But it was a real PITA getting it fixed. I've heard other horror stories where people never got a clear title. You don't want to mess around regarding matching numbers. There could be liens or something was stolen.
Thank-you LandPimp--I forgot that the late-model US-imported trucks that actually got a real VIN did also have a dashtop strip-plate.
We so often just throw-around the "word" VIN, when most of the old trucks simply had serial numbers back then.
Because the firewall, doorjamb, and dashtop plates are riveted(including the early plates screwed to the fender) and easily removed, I think in the US, Feds still count the stamped frame serial/VIN as the vehicle number they want to see from the factory; no matter what country his residence, the fellow originally writing here should have at the bare minimum that frame number match the legal paperwork.
As to any missing ID plates, he should check with his national and state/province authorities as to their additional requirements for registration; all this before any money changes hands. Some US states will create new VINs, but that's another whole topic.
titles go with frames, as long as the title he is providing matches the number on the frame you are good. Many of these have had their bodies rusted out and replaced. If there is no number on the frame where it is suppose to be that is a huge red flag.