axle change? front to back?

Ok I know there has been much talk about disconnect and stuff to the rear axle's. I can't do this but can you just take an air-shift front axle and replace the front rear with it? I am not sure of the distance right to left if it end up wider or not but not sure if it will matter if you change to singles also. I would think you can weld or bolt the steering linkage in a way so it does not move? And the just tie in the air lint to the front or another valve to control it. I do not know if this will change the carry capacity? Front cap. vs rear axle? Is it the axle or springs or something else or both? This is just an idea that someone may of already thought of as a less expensive way if you have an extra axle or two laying around. Yes I guess you could do it to both? Then you can control which if any axle is driven. The only problem I have thought of if this is done to all axles would be parking brake.... or lack of one. If I am right no air means axle is disconnected right? so if it sits and looses air the parking brake on the drive shaft would not hold? or does it stay engaged  till switched off? Not sure if its spring loaded to keep engaged or not, but that would only be if you do both anyway. Remember this was just an idea... I am running for cover now..