^ I couldn't find any technical specs based on the part # and it's too old to assume it necessarily corresponds to anything in JBL's current product lines, let alone that it could be an altered design for OEM use.
I wouldn't chance it, would stick with same 8 ohms as was in it. It might help if you posted pics of the speaker box. I vaguely recall someone stating it was bolted to the back but I don't remember if that was the same generation or newer Explorers.
It looks like there are three indented areas around the perimeter of the speaker. If those areas don't allow access to mounting bolts then you probably have to pull the whole box out which will require taking the interior trim panel off first.