I cringe at someone ruining a bronco that way. I bet a whole lot of ford guys would, at the best, give him dirty looks on a regular basis.
That being said, for what he wants, you are dead on right about using the crown vic front end. It will simply work better. Having never slammed a vehicle myself, it may be a little bit more work, but I know it isn't terrible to do. Plus those are easy to obtain.
If possible though, please do us all a favor and take this truck away from him/ replace it with something, anything, else. Maybe explain how he is completely ruining any resale value?
Resale value??? Of a '86 Bronco? Those trucks are only worth a bit more than their weight in scrap these days, if it was an OBS then yeah, maybe, but anything between '80 and '91 is not gonna bring any decent money unless you find a buyer who just has a passion for these trucks. On the other hand a tastefully modified truck (even if it was done on a budget, as long as it was done well and safe) is much more likely to sell for more moolah.
What other Ford owners think is completely irrelevant, this is not THEIR truck. Every time someone questions my vehicle mod choices without any technical backing I ask them how much money they have in MY project - oh, zero you say, well then, that's exactly how much your opinion is worth to me! God I wish people would just mind their own business, instead of criticizing others for what they do with THEIR OWN stuff. Applies to opinions expressed on this board as well, if someone feels hurt that's too bad - just cause someone doesn't like lowered trucks doesn't mean EVERYONE else should also feel the same way. The OP wasn't asking about what anyone thinks of his friend's project, he was asking for tech info, so how about we keep our opinions to ourselves and modify OUR OWN trucks as we like, and give the OP what he wants?
Now that I have that out of the way, here's the relevant info: yes you can switch between 2wd and 4x4 on a halfton chassis by simply unbolting one set of beams and radius arms and replacing them with the other. No changes are needed in any of the brackets riveted to the framer, the same steering linkage will also work with either setup. There's about 2" difference in ride height, so losing the 4x4 will lower the front by that much. If that is where the Bronco owner wants to stop then he will need to just drop the rear by 2" at most. If the truck has the 1.5" lift blocks in the rear just pulling those out should do the trick. If lower ride height is desired, it's time for Dream Beams in the front and axle flip in the rear. I'd advise against simply pulling leafs out of the rear pack, as while that lowers the ride height it does so by softening the springs, and softer springs will also wrap easier when he lays into the throttle hard. Well unless you get into traction bars and such, but that's beyond the point here.
The mention of resale value does have one good point though - if lowering the truck was done via some major surgery like the Crown Vic suspension, depending on the quality of execution, it could either up the resale value or completely tank it. "***** fab" (borrowing a Pirate term) is what I'm thinking here, has all the right parts and ideas but lousy workmanship - not knowing the particular Bronco owner's skills I'm simply stating the worst case scenario. On the other tried and true bolt-ons like the DreamBeams will pretty much always up the value some, partially because they are so simple that it's pretty hard to screw them up even if one tried, and also at the same time they require other supporting work (new bushings and likely ball joints for example) that the new owner won't have to worry about doing themselves in the near future. Additionally, with the bolt-on stuff, if one changes their mind and were smart enough to keep the factory parts they can switch back whenever they please - however the Crown Vic suspension, once on, is not going to come off easy. So keeping the 4x4 parts around is probably not a bad idea, even if they end up just sitting in the corner of the barn under 3" of cobwebs-reinforced dust.