Are all a body ball joints screw ins?

I would say most likely. All you can do is to try to screw the new ones in an see if you are able to archive the proper torque spec. I think its 125 ft/lbs. If you get close to the spec, but can't reach it then you could maybe tack weld them to retain then in the control arm. You will need the special ball joint socket to do it correctly.