BB,
at least you kept your 600's! I did a very silly thing & sold my 7x64mm to a mate who since past it on to a member here (I think)?
You should be able to open up the 600 to take a .404, mine could take lengthen 7x64mm - projectiles seated out with an OAL of 87mm, you need 90mm for the .404 so if taken off the back end of the action it could be possible?
Best of luck finding a 602.....like 'rocking house sh!t'