I wouldn't even THINK about welding the front diff. Don't do it, there will be many situations when even offroad you won't be able to steer.
I have f/r air lockers & just 4 weeks ago I was in a nightmare situation where I was close to doing a forward end-over rollover because I couldn't steer the correct direction because I couldn't unlock my front air locker. The trail was rocky and most of the Jeep's weight was on the aired-down front tires, there was too traction & pressure on them for them to be turned left or right. My Jeep was descending down a VERY steep trail & I had to make a hard right turn down the fall-line to avoid that end-over rollover but I couldn't, there was too much pressure on the front locker for it to unlock which turned the front axle into a spool... like having welded spider gears. I was finally able to back up enough so I could take the pressure off the locker to unlock it so I could make the required turn.
Weld up the rear spiders if you want but leave the front spider gears alone.