The narrow track front axle from 80-82 or 85-91 models will be a bolt in
What Flint said. Best and simplest advice.
I never dealt with this on a FSJ but did on Dana 30s in YJs....They make mechanical(pto style cable) shifters for them. The one thing that might be relative and this is why I say I don't know for certain.....Dana 44's typically have the seals for the axles inside the diff housing....Every one that I ever saw has that machined surface on each side, just outside of the diff carrier bearings. That is how all of them seal the axle shaft on the FSJs. I am sure that is how it is on the right(pass) side of your jeep. That being said, I would almost think that one could use a solid one piece axle on the driverside, if you can go inside and install that seal and there is clearance for the one piece after you remove the guts area of the vac disconnect.
I certainly heard of Dana 30s being done this way by using a XJ jeep right hand shaft.
Driveshafts for all Jeeps, Constant velocity rebuilds, Replacement, Repair
Putting this back up. "Someone is gonna have to crawl under the rig"