Hey Gil
the 255/100 is expensive here too, about 300€ is a good price! You will get it at any truck-tire-shop. And yes, we always travel tubeless.
It´s a perfect touring tire with wordwide availability and very good performence on piste, lava, rocks etc and even on road. But it is not very good in sand and dunes and the HZJ78 will be quite high and tippy..The spare tire has to go in the car or on the roof, even a kaymar will not last with the weight on piste...
And the whole set up will not be heavy duty!!
The gearbox form 78 and 79 likes to brake.
We fitted 4.88 Diffs, in the front a spacer ring is needed, further OME Heavy Duty and the front fenders need some "remodeling" (not for the use of old 9.00XS, than a hammer will do
)
To get it street legal we had to limit maximum speed to 110km/h (speed index K and no M&S signature)
With carefull driving we had no problems, but we decided to start all over with J80 technic and 325/80 (in case of emergency a 255/100 spare will be just 1 cm smaler)
A friend of mine solved the gearbox problem of his 79 with the stronger 5 speed box from a J80, it fits nicely to 35" with original Diffs..