I have an 89 f150 4x4 and i am running 32's on it now and seem to have plenty of clearance, and i do believe that i could fit 34's on it with a 2 inch body, but i need some input and FACTS about the situation.
BUBBA

 

My buddy has a 89 f150 4wd with just a 3in body lift and hes been running 35x12.5 in pro comp all terrains on 10in wide rims with just a little rubbing offroad.I use to run 33x12.5in BFG all terrians with no lift on a 87 f150 4wd.The only thing with the LTBs is the size of the lugs.They might rub a little on a full turn but that should be about it.I'd do it

 

should be able to clear them, how wide are the tires? and most importantly what are the specs on the wheel you are using?

 

well i powder coat wheels at my job for tractor trailers and i have stock wheels on my truck, i am either gonna powder coat mine black and use those or summit has some 15x8 black steelies for about 50 a piece, but for now most likely just the stocks.
and the dimensions on the tires are, 34x10.50x15, im not to crazy about the whole 10.5 thing but for some unknown reason they dont make a wider size than that in the 34's, they make 13.5 in the 33's, a little strange to me.

next question, what is the easiest way to check the gear ratio in my truck, because i do believe that the owner before me put 4.10's in it, because it has a low 1st, and 2nd gear, hell in 3rd gear runnin between 2500-3000 rpms, im only topping out at about, 30-35.