Thank you for putting this in the right section. There are many options for putting a solid axle under your truck. The most common is a D44 from an early 80's jeep wagoneer. Avoid vacuum disconnect axles though. This will maintain your WMS - WMS wheel mounting surface. This is probably the cheapest and will allow you to run around 37's with upgraded shafts. More serious rigs use dana 60's from 78-79 fords, although most ford axles can fit with some extra work. This will let you run almost any tire you want. You can also have custom axles made for use with any type of combination of centers and outers.
It also depends whether you will run leaf springs or a link type suspension. There are benifits of each.
As for the ride it depends on how well the job is done. It will be hard to beat the factory ride from your truck. However a proper SAS will ride much better than a maxed out IFS lift. Biggest issue here is that most IFS lifts change the geometry of the suspension which lead to a ride that is not what the factory intended. Lastly the SAS will require more maintenance, but be more reliable in the long run if you wheel your truck hard. IFS will get real expensive when you start messing with it too much.
Also there are tons of info on the board about the issue. If you spend about 100 hours searching and reading you will have a much better understanding of what to expect.
It was jeeps way of disconnecting the axle shaft from the diff. Similar to the ADD system on the toyotas. I believe the purpose was to allow for auto locking hubs for a shift on the fly type setup. The d44's that have this have a vacuum tube coming out of the diff.