Install zerk fittings in Ford E-350?

I will second j-d's comment about being careful not to blow out the boots. Blowing a boot, and thus allowing grit to get in, may be WORSE than not greasing. I could tell you how I know that, but the memories are too painful*.

Examine the movement of the steering and suspension, and make sure you don't install a fitting that'll be snapped off as the front end goes through its movements. I had a car on which the U-joint could not accept a zerk fitting in use, because it would be snapped off or interfere with movement of the joint. I had a setscrew plug in that one, and the greasing kit included a long L-wrench and s suitable open-end wrench, so I could remove the plug, install a long zerk fitting, grease the joint, and put the plug back in.

*I started in the wrenching trade, in which I spent a few years, just as the boots started to be sealed to the tie rod ends. Before that, they were just loosely fit, and you ran grease in until it oozed out the lip of the fitting. A lot of old-line mechanics got yelled at for greasing the joint until the boot's seal popped; they were used to seeing grease.

Yes and Yes

Replaced the ones on the steering with angled ones that made them easier to get the chuck onto. Added angled ones to the four ball joints. Grease till the boots swell and stop. Blown boot's about as bad as not greasing.

Which may be why the latest Ford ball joints don't even have that plug any more. NO greasing those puppies.