I am thinking of swapping out my 302 for a 460 in my 91 F150....
What all would I have to do to prep the engine bay to accomodate<(sp?) the 460?  

are you going with a complete 88-97 efi 460? you need the frame horns or motor mount supports from a donor F-250 or F-350 wireing harness,computer,radiator tranny basicly a donor truck with a 460 in it.  

You could achieve a big boost in performance with a 351 and a set of deeper axle gears. Even the 302 would wake up with deeper axle gears. Given todays fuel prices and a 460's thirst for it, it is not the wisest swap to do.  

Like how tall of gears wirh a 351 swap??  

That depends on tire size and tranny as there is no single perfect axle ratio for all combos tire sizes.  

If you have 1/2 ton running gear I would stay away from the 460. I would stroke the 302 to 331 with nice heads and nice roller cam before I installed a 460 with 1/2 ton running gear. A good 460 will find your weak links. There is no modification to truck with a more efficient small block. But if you want to go big block you engine swap is the cheap part. Axle up grades driveshafts and other related componets. tranny and clutch if that is your application. most times you don't need the big block but its nice having the big motor to.  

I would swap a stroked 351w for the 302. Almost a direct swap, more power and cubes than a stroked 302, and less weight and mods than a 460. I don't know for sure, but I think you need new motor mounts and tranny/bellhousing at the least w/ the 460. Probably different radiator, definately different exhaust. You can stroke a 351w to 393 for cheap with a 3.85 stroker crank, stock rods, and 302 pistons.