Not only is there a concern about breaking rose joints but it is not unusual for the rose joint to transfer vibration into the front mounts and have them crack. Remember if you make something stiffer it usually means you have to beaf up the mounting points because they were not designed to take hard mounts.
If you are concerned about breaking the standard castor rods then find some castor rods out of an early LJ Torana and mount those into polyurethane bushes. LJ rods are not only longer but are much thicker in their diameter and I've had them on my rally car for years and never broken one even under the most trying conditions. To fit them all you have to do is drill out the mounting holes to a bigger dia and bolt them on and set the castor to your requirements.