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If the Scout 80 you are looking at still has it's original axle set, they will be Dana 27 units. 35" tires used in serious off-road use will eat those axles fairly soon. So an axle upgrade should move to the top of the project list. You can see this is a very common question around here.
An axle upgrade should also include a spring-over suspension conversion which will allow clearance for virtually any size tire as long as the engine can turn 'em.