As for the oil coller itself, I would, any day of the week, fit an external (stand alone) Air-Oil-ATFoilcooler
The danger of polluting the AFT with antifreeze is not to be taken litely
Reg the intial Q; I took out my rad the aother day when I replaced the engine (see separate thread) & topped up with abt 0.5l when refotting it. I did clamp the hoses though while disconnecting.