If it's on the front frame horn, and starts with a letter such as "C" or "D" (example: D4TZ-******) then it's the engineering number of the frame.
If it's just below the firewall on the passenger side however, and starts with a U13, U14 or U15, then there's an issue with a mis-match.
Paul
You could start by seeing if this site pulls any info on either vin:
https://www.nicb.org/vincheck
There should be a star at the beginning and the end of the vin numbers on the frame. What's the location of the one you're looking at? Top side of passenger side frame rear of the starter, almost under the passenger floorboard. There's another one rear of that but difficult to see with the body on. Warranty plate is on the driver kick panel on 66 and 67, and on the back of the glove box door 68-77. Door jamb stickers didn't appear until 70' iirc. What year is your bronco?
You could start by seeing if this site pulls any info on either vin:
https://www.nicb.org/vincheck
Depends on which state you live in and luck.
Another member went through a nightmare, while others have corrected it fairly simply with their DMV.
But wait for more to chime in on that aspect before you go down the legal path.
Paul
If you swap your frame, pretty much in any state you're supposed to get it re-registered to match. Same if you purchase a new frame with no serial number. The state DMV will often create a new VIN that is your new identification moving forward.
Whether they go to the trouble or not, depends on where you live.
Not sure what happens when you don't match the warranty plate in the glovebox or the certification label on the door jam ('69-ish or '70 and newer) and someone checks because some DMV inspectors will only look where you show them, or where the numbers are easy to find, then argue that those can't be a legit VIN because it's too short.
Then you get to go through that rigamarole too. Don't know what they'd do if it didn't match, but you'd probably have to jump through a hoop or two and speak to just the right person at the DMV office to get it cleared up.
And hope that the body was not stolen!
Some states are more detailed than others, so some are less hassle too.
And there are a lot more details than I know. Some members are really versed in this so listen to what they say whenever they pipe in.
Paul
The nightmare turned out great. Better than some could expect I imagine, as the help of a friendly cop turned the tide if I remember. About ten years go now maybe?
The project was finished with a ton of money put into it before registering. As soon as he took it in to register and it came up stolen, he almost lost it all.
Due to a lot of hard work (and almost a year if I remember?) and the fact that the insurance had paid off originally, and the old owner did not dispute it I don't think, the result was he got the Bronco back with a clear title. Maybe a salvage? No, I don't remember that as part of the story.
But it did work out. Plenty of white hairs showed up from that one though!
Paul
Paul
I don't remember if you said, but does the title match the glove box at least?
Paul