Hi Netty,
you could refer back to the GP and have investigations. However, you really need to correlate any ivestigation findings with his clinical diagnosis. If you are thourough with your cinical assessment, then it should be enough to get a good clincal picture of his condition. But just remember that with such a patient i.e. elderly and with chronic history, his overall presentation will most likely be a combination of various contributing factors such as foraminal narrowing, stenosis, general disc degen etc....so don;t just look for one thing.
Without actually assessing him myself, it is hard to say what he would benefit from. In general, improvement of intersegmental mobility through passive or active strategies will help the situation. Have a look at areas such as his hip flexibility and movement strategies that he tends to use to get around.
Hope this gives you some ideas.
let me know how you go.