I'm looking at putting a solid front axle on my truck. 90 Z71 single cab sb. so what has me concerned is will the existing 4wd driveshaft bolt right up to a solid axle if i put one in? or will that require mods as well?

 

Check out my SAS thread in show off central.
To answer your question it depends on the transfer case that you have.
Mine had a 241 with a yoke connection and I needed to buy a conversion flange and a new drive shaft. I did just help put my old IFS lift on an 89 2500 that had a flange connection on it already. Mine just wasn't made for much of an angle because the IFS differential never moves.