It all just depends on what you will be doing with the truck. If you will be doing highway driving, I would stay away from anything 4.56 or lower with that th350. If you had overdrive, now thats a different story. It also depends on how often you drive your truck and what you want to do with it. If you dont drive it on the street much and want to rockcrawl with it, then 4.56's should be plenty of gear. Oh, and also, before you buy front and rear lockers, you might want to look into some beefier axles first. Locking that rear 10 bolt with 35's=breakage. You can pick up a 14ff at a junkyard, already with 4.10's, and some even have 4.56's if your lucky, for way cheaper than a locker. You could go ahead and buy the locker, but it will always be on the back of your mind when your wheeling it, that the 10B might break. You will probably end up putting more money into keeping that 10B happy, then you would buying a 14ff, and a locker. Since you going to pay for re-gearing anyways, why dont you just buy a 14ff, re-gear it to whatever you decide, and hold off on the locker for a little while. You will end up thanking yourself in the long run.
-Harrison