The lower ball joints are spot welded on.
Will I be able to get away with just press fitting the new ones in or will I have to spot weld them once they are in place?

 

I've never heard of the ball joints being welded on. They should just be a pressure fit. In which case you shouldn't have a problem pressing them in place, providing you don't damage the housing removing the old ones. I have never owned a 94 2wd so without seeing what you are working with I'm not sure of an exact solution.

 

Yes, I'm sure some joints were welded on, either by manufacturer or after the fact in repair attempt. Carefully rewelding with wet rag and very short welds should cause no problem.

 

It was just tacked on 2 spots.
Probably why NAPA also sells the lower ball joints with the lower control arm.
Not worth the extra cost and work.