I went with the Ford/Visteon 4.30 gears. I was told by several shops that given the choice, they would pick the Ford gears as they are of better quality than any after-market parts. None of the shops I called sold the Ford parts so I'm pretty sure they were being honest. I didn't want to risk having a noisy gear set due to poor machining. (Real tomato ketchup Eddie? Nothing but the best!)
I also put in a Detroit No-Spin locker. The stock limited slip worked great in my truck, unlike all the people here who complain about it, but when one of the rear wheels was off the ground, it was very difficult to get the truck moving again being I don't have a 3-wheel drive. With the Detroit, that isn't an issue, it'll move, period. Plus the power slides are ridiculous now. After a few thousand miles, most of the clunking and roughness associated with automatic lockers went away. I guess it needs a good break-in too. An ARB air-locker might have been better since they are easier on the drivetrain. I haven't noticed any extra tire wear either. (Compared to the limited slip.)

Be prepared for some pretty good acceleration with the 4.30's. I swear this is true, but I smoked some kid in a 95 Honda Prelude from a dead stop 3 weeks ago. He thought I wanted to race because I let my truck roll back. He didn't realize that at my age, it's not that I want to race, it's just that I am too senile to remember to step on the brakes when my transmission is in neutral. This high-school punk was revving that thing up and letting it roll back too, while giving me "the look" but somehow, he only succeeded in achieving lameness since he had an automatic. It was "pants", as they say. I did a 3-5-6 shift and he got "owned" by a damned 5.4L F250! A farm truck! Not even a real man's truck or anything. (Not a diesel) He had a fart can exhaust on his car so I heard him at full open throttle the whole time, but the noise kept getting lower and lower... He should be ashamed of himself.

But I digress, the gear set part number I got was 3C3Z-4209-CA. That part number was for a 2004 F250, I'm not sure what year your Ex is. (1978 I think?) They probably have some updated part numbers for later year trucks.
They were pretty hard to find and also expensive:$400!!! I think it is because I got them from a Ford parts warehouse. BFR250SD said you could get them cheaper from West Coast Differential or Randy's.