I'm with Mart on this one Andy. Although it won't make much difference when you adjust the angle of the stuffing tube (unless you bend the stuffing tube to follow the angle of the stinger - which you sometimes have to do anyway, for more than slight adjustments), you also, ultimately, want the facility to be able to move the whole stinger up and down. As a general rule of thumb, leave at least two inches between the transom, and where the stuffing tube is fixed. As it stands now, it should be fairly easy to chop some of the epoxy away. Perhaps even more importantly, when you rebuild the bottom of the radio box, make sure you leave clearance there. Different props will work best at different heights. The chopper props, for example - which are becoming popular for fast monos, are designed to run on the tips of the blades. They are reckoned to run best with the centreline of the prop ~25% of the prop diameter above the vee; so a 70mm prop would have the centreline about 17.5mm above the vee (or ride pad in your case).
I know that; with a nicely fitting hole for the stuffing tube, and nice small holes for the stinger fixing bolts, you can't adjust the stinger upwards as it stands, but those things can relatively easily be adapted. If the stuffing tube is fixed solid all the way, and there's no clearance under the radio box, it will make life much more difficult.......