With the axle disconnect the 97-99 have, a welded front diff shouldn't be an issue until you engage 4wd (assuming everything is working correctly). The models without the disconnect will need manual hubs to disengage the left and right sides to avoid binding during turns
Locked front differentials are hard on cv axles when your turning, the sharper you turn the worse it gets.
I'm going to try to install a ford 9" mini spool on the rear axle of my truck. Axle diameter and spline count match up, so here's to hoping. Sadly it looks like the front axles are slightly smaller diameter even though they are still 28 spline. I'm going to test fit anyway just to be sure