On any AWD car/truck it is very important to have the same size and type of tires on the four corners unless the car/truck was engineered that way. With that said... Ever see a car running around on those fake spare tires? As long as you are not taking a long trip with the smaller spare on and realize that you can not emulate Speed Racer with it on, it should be fine. if you use it as a spare to get to a location to fix or replace the busted tire you will be fine with a smaller tire.
I am doing a 110 Double Cab project. I am planning on doing the spare on a swing away carrier. I have had the smaller tire on the hood of the 90 and couldn't stand the thing in my vision. Off road it was horrible.
Land Rover 110