will i need a smaller differential for a set of 4.10's on stock diff?

 

you should be able to buy a set of 4.10's for the stock differential size if that is what you are asking

 

No you can use the diff thats in there. Keep in mind the 10bolts are not strong and 4.10s are thinner and more brittle than stock gears. If you plan on drags radials, adding lots of hp, or launching at high rpms you can kiss that rear end goodbye.