I think the 7402 is the special DA 8-speed uniglide hub that is compatible with nothing else. The 7403 uses a special DA specific freehub and normal 8/9/10 speed cassettes. You can change a 7402 into a 7403 if you have the special tool and can find the special freehub.

I have a 7402 wheelset and was trying to convert it to 7403 for awhile but it seems to be easier to find the 7402 cassettes than the special freehub so I think I'll just leave it as-is and try to stash a few spare cassettes.