Technical School is in, Chev parallel front end setup

In the drawing, it is raising the drag-link /pitman balljoint that improved the situation [not moving it forward].

With cross steer a Panhard bar is more effective than a Watts linkage .
A watts linkage only allows vertical movement and the roll centre pivots at the centre of the bell-crank.
So with body-roll [rotation around this pivot] it will induce mechanical bump steer.[the opposite wheel will toe-in with rear steer tie-rods]
This is caused by a long arc of the drag link combined with a short arc from the axle centre pivot point.

Basically a cross steer drag link is a panhard bar [with attachment points on the steering]
By adding a panhard bar to the axle, they both act together as a parallelogram.

 

If you want to save yourself the cost of a dropped axle mount the the axle on top of the springs like they do the rear... Just make sure the spring doesn't interfere with the tie rod or steering rods...

 

1-Wider/longer are two different things as it pertains to springs. Wider will reduce spring twist or deflection, but longer will increase the odds the spring can deflect. But longer also allows for a little better ride. Although even shorter springs can give a good ride if the right spring rate is maintained. It's not a case of a certain spring being perfect, and sometimes after you've got it driving you may find you need to remove/add a leaf or two to get the perfect ride that's softer or firmer.

2-Fixed end is not always the back, although in a side steer setup the fixed end could be either end of the spring. In a cross steer it's best to figure out which side of the axle your steering box will be, and then put shackles on the opposite end. Shackles on the same end as the steering will mean your pitman arm and tierod will be pushing the against the shackles which causes deflection, and vague steering. By having shackles on the opposite side of the steering your axle will have less deflection.

3-Longer shackles are never an advantage. Longer shackles mean greater chance of deflection, so keep shackles shorter. Not too short where they don't work, but as short as is workable. On lighter vehicles I prefer 3"-4" centers on the holes. Also be sure to use a thick material. I use 3/8"x 1.25" for my shackles on cars and light trucks. Your larger vehicle will require larger and thicker shackles.

4-Flatter springs wont deflect as much as springs with a lot of arc, so flatter is better. Most large trucks use very flat leaf spring packs.

5-Yes, too much drop can have negative effect in braking and spring wrap. I can't tell you what that is on a large truck, but on most cars and trucks a 4" drop isn't an issue, and many makers used this as OE on their axles.

6-Swaybars are always good, but depending on how stiff the suspension is they might not do much on firmer setups.

7-Shock angle varies and there's no perfect angle. Straight up gets the maximum out of shocks, and the greater the angle the less effective the shock is. I'd never go past 30 degrees, and I try to stay 20 degrees or less on my solid axle installs.

8-Side steer or cross steer is your choice. Side steer gives a longer drag link, which will decrease the amount of bump steer over a shorter side steer tierod.

9-Caster and camber have not changed as it pertains to solid axles. What worked for decades, still works. Use the old standard of 5-7 degrees kingpin angle, and 1/8"-1/4" toe in.

10-Keep your mounting points as low as possible. The higher they are, the more likely side forces will affect the mounting, and give less precise steering.

 

If it was mine I would do it like this

Inspect the front end for worn parts, king pins, tie rods, don't forget the steering box. Replace parts as necessary
New gas shocks of best quality
Remove springs, clean off rust and dirt, polish with a disc grinder. If the tips of the springs have worn notches smooth them out. Paint with POR 15 and put the spring back together with new sliders. If you are not carrying heavy loads you can leave out a few leaves to soften the ride. Or if necessary have the springs rearched or replaced by a spring shop.
Adjust steering box to take out play if necessary. Follow the factory repair manual on this.
Front end alignment. You may have to go to a truck shop to get a beam axle aligned. For the finishing touch you can have it set up with minimal caster angle. This will sharpen the steering and make it easier to steer. If you do this you must add a steering damper.
Don't go too wide on the front tires and pump them up to 32 PSI.

I have done all this on a beam axle pickup truck and got a very satisfactory handling and ride, at least on decently smooth roads. You shouldn't have to replace the steering box or do anything too radical. While you are at it check the rear springs, spring bushings and put new shocks on the back. You will probably want to recondition the rear springs same as the front. Only you may want to put on air shocks if you remove rear spring leaves. Just in case you want to carry something heavy once in a while.