How Big?

A bud of mine is running 33 x 10.5" wide on an uncut with a 2.5" lift. Just don't run over 10.5 wide and you can limit the up travel with larger bump stops if you have issues.

"what transmission shall I run?"; "should I get higher lift rockers?" what tire to run? are all Q that are answered by the standard automotive: "What is the APPLICATION?" Final application is everything simply because the vehicle is a system- change 1 thing 1 place it effects the others.

Here every rig is different. Non-stock bumpers, spring age/sag, other mods (drivetrain weight, etc, etc) effect. Then we get into use - mudder, mall craw, street, off rd - esp important to a true multipurpose like the 1st gen (not good at anything, OK at several). Then we have tire-applied-to-rim-width to consider, tire aspect, etc. Sometimes more detail assists (actual tire co & model). A 31 9.50 @ 15 seemed to B a standard most uncut, unlifted rigs could use. I can not find the same in a 33 I used to use @ 1BL, 2.5SL. Now we have the KO2 which the tire blocks R too lrg in my opinion (& still is not made ina pizza cutter which is my choice for the off rd sno here).
/OR/
Short Answ: it depends...
(Y there's no sticky)

Yes 31" will the biggest tire, if you want to install a bigger tire the only choice is using a ford Granada rear end this will bolt on is narrower and is 9" with factory disk breaks good luck