Axle gearing is particularly important especially when going with larger tires or creating a truck for off-road purposes.  Here is a general guideline for axle gearing related questions.

All Land Cruisers came from the factory with 4.11 axle gearing other than 1979 and later FJ40 models and all FJ60 models which came with 3.73 axle gearing.
In 1988, FJ62 models were returned to 4.11 axle gearing.

For upgrades to FJ60s, use this guide to have 
your axle gearing returned to stock ratios:

Stock 235 tires = 3.73 axle gearing
31" tires = 4.11 axle gearing
33" tires = 4.56 axle gearing
35" tires = 4.88 axle gearing
38" tires = 5.29 axle gearing*

*may require some grinding into the axle housing.

These gear ratios are approximate and will not bring your gear ratio exactly back to stock ratio but they should be somewhat similar.

It is also widely recommended, particularly with lower output engines (F, 2F, 2H, B, 3B) to run one axle gear lower for more power.

For applying gear ratios to 4.11 ratios, use the same guide above but skip ahead to the next level.