Nope, direction doesn't matter. As long as you've got an out-with-the-bad, in-with-the-good situation, and the manifold vacuum is hooked to the valve, not the breather, you're OK. I guess they went by which side was convenient on each particular application. I'm guessing though.
Hey, Frustrating is a Bronco's middle name sometimes.
Sounds like you're on the right track with looking for vacuum leaks and such. I'm assuming that you tried adjusting the idle up with the screw and didn't have any luck, but if so, what did it do then? And have you had a chance to mess with the mixture screws? When it won't idle, it's kind of hard to adjust them, but sometimes just messing with them will net you enough improvement to keep you going.
It sounds like you may also have the vacuum advance hooked up to the wrong port. On a setup like yours, you have to have it to a ported vacuum source and those are "usually" up higher on the carb. The lower ones are usually below the throttle plate and get full manifold vacuum and the ones above get their signal from a slot adjacent to the throttle plate so it only has a vacuum signal AFTER you start to open the throttle.
Some vehicles DO use manifold vacuum from the factory, but most by far, including the Broncos use ported spark.
At the very least, if you're not sure what this one has, disconnect it temporarily while you're messing with the idle.
Also, check for a VERY good spark. The leaner you get the harder it is to ignite the mix, so a good spark is a must. Which ignition system are you using?
Those are a few thoughts I had off the top of my head but if anything else pops up I'll throw 'em out there when I get back.
Good luck.
Paul