I have done it on our own and plenty of customers bikes. Its a piece of piss..... remove the 600 caliper and hanger, throw the original 600 caliper in the nearest canal, place the 1000 caliper onto the 600 hanger and you will see that it doesnt quite fit. if needs more clearance on the "arched" section between the two bolt holes.
take a half round bastard file (no seriously) use the curved edge to file away at the arch, it doesnt need much so remove section and then keep attempting to fit the caliper until it fits, removing just a little each time. when the caliper fits the hanger and bolts to it then you can either refit to the bike as is on clean up the file marks with increasing grits of wet and dry until smooth (I dont normally do this bit as no-one is ever gonna see it.
Job done