Finding a Ford Fiesta basic specification circa 1984 seem to be rarer than rocking horse do do, if some measurements could be taken even now, it would answer a few questions.That's right - you could infer a minimum but not a maximum. If Fiestas were designed to fit a maximum 6' driver then the seat position being all the way back probably tells you only that the driver was 5'11" or more. Interesting but not that informative.
I still want to know how tall JC is.if he's too short to have driven the Fiesta with its seat in that position, I doubt we will ever find that out, for obvious reasons.
I'm 6'1" and owned a Ford Fiesta MK 1, I seem to recall that I didn't need to have the driver's seat all the way back.
But it was a long time ago.