31's are not as tall as your stock tires

 

the stocks are 265/--/16 right? it didnt have the stock tires on it or stock size the guy who we got it from had smaller tires on it and they were shot.... we put my buddys old mud tires on it for the time being since they were still good hes getting new tires for the wide rims and taking them back i belive

 

stock tires are 235/85/16
they are about 31.7" tall.
if you want 4.10's and 35" inch tires,then you will need some aftermarket gears close to 4.50:1
since its 4wd.you will need to change both gear sets front/rear.

if you drop 4.10's in the axles,and run 35" tall tires,it would be close to having fords 3.73's
if you keep your 3.55 gears and put 35" tall tires,it would be closer to fords 3.08's (little lower,like 3.20,but would basically feel the same.not what you would be after for towing 12k lb trailer.)

 

is it really a complicated job i can pretty much just change the gears out not alot of work required on other areas of the truck is there

 

its not easy swapping gears no.you should really have a reputable shop do it for you.they have the tools required.

you need to figure the price of the truck your looking at,and if it doesn't have the gears you need,you need to add the price of the gears and labor to see if its worth buying the truck,or keep looking for a truck with lower gears already.

lifting trucks and putting on big tires is just a very expensive proposition.you have the price of the lift,price of new gears,added price of larger tires,labor costs for the stuff you cant do,and less fuel economy.it costs literally thousands of dollars difference in the ownership of the truck over keeping stock tires or smaller.
lifting the D50 for 35" tires isn't cheap either.it's not like the D60 in the f350's.

i think you'll find it MUCH cheaper to keep looking for an f350 and lift/gear that to start with.

 

we already have the truck and the guy i pretty much live with who got the trucks is a diesel mechanic and works for john deere he has any and every tool we would need to do pretty much anything except for a full lift at the house....

 

so if im going for it i just need to order the ring an pinion for the front and rear plus gaskets and oil thats pretty much it right.... im already going to be dis assembling the front differential for new bushings anyway so should just do it when i do that right?

 

Well F250 already posted a link on how to do it, so let us know how it goes. Pics and progress photos would be nice, along with what it is costing you. Sounds like fun! Good luck and leter' rip! LOL