Regarding tyre sizes, when I got my 1993 Disco it had Michelin (XPC?) tyres. They were sized as 205R16. I think that this means that they are the "full-size" profile, which I think, approximates to an 82 profile and so your 80 profile guess is just about spot on. They were on 7" wide rims.
IIRC the difference in rolling diameter between 205R16 & 230/70R16 is less than 1% (ie: "stuff all").
HTH,

