Woldan,
I have used a CZ550 standard length stock to replace a ZKK600 stock.
There is a little little work to do, but basically just relief work. Mine I had to do around the front of the magazine well on the new stock, the 550 action itself is only very slightly different - not much but it caused the action to rock initially.
There is a wider spacer on the front screw between the bottom metal & the action on the 6oo's so unless your replacement stock comes with this new spacer then it will have to be redone bigger as well.
With the 602 & 550 magnum stocks they will both have the barrel lug arrangement, where as the standard length action will require the 600 to take off its barrel bolt arrangement as opposed to the CZ550 stock which won't have that arrangement.
Apart from that it is pretty much drop in, but I'd still do a bedding job as well for a .375 & up