Dave Johnson, one of the head engineer/designers at First Texas posted this in answer to this question...
"The 11 inch DD originally developed for the Fisher F4 should work just fine with Time Rangers manufactured since 2004. Make sure you're getting the searchcoil with the push-on connector, not the screw-on connector. Compared with the 8 inch searchcoil you'll probably see a slight increase in depth and a substantial improvement in target separation."