Hi and welcome to series ownership challenging and satisfaction guaranteed in equal measures
Being 4 wheel drive when selected it’s important the rolling diameters are the same on front axle and rear axle if you are driving 4wd on tarmac this reduces transmission problems but that said normally 4wd is used off road on loose/ soft ground and or snow so wheels can slip when they need.
The 80 spec is the aspect ratio , are you saying the other two does not have any aspect ratio
perhaps post some pics of each so we can see the tyre markings
There will be peeps on here who are tyre experts but I’m not one of them
I have 7.5 x R16 on mine quite a tall tyre that gives good ground clearance
Workshop manual here which has tyre wheel section And a general good read
http://www.retroanaconda.com/landrover/2010/03/series-iii-workshop-manual/