Yay. I am moving to Java 1.5, WebSphere 6.1 and most importantly, IBM Rational Application Developer 7.0 for WebSphere (RAD 7.0). Unlike its previous version which bombed when trying to install the Subclipse plug-in, RAD 7 appears to have survived the transplant.
Follow the instructions – note that RAD 7 is appears to be based on Eclipse 3.1 so use the links to that update site and not the ones for the more recent version of Eclipse. Modern, not.