Please, does anyone happen to know the correct packing size for the stuffing box on a 1978 Islander 28 sailboat? I've found plenty of good information on this site and elsewhere on how to do the repacking but the packing size is very hard for me to gauge. The shaft diameter is ¾" but I'm having difficulty measuring the diameter inside the compression nut because I can only slide it clear by less than a half inch before it comes up against a key on the engine'shaft coupling. The key won't move. Ideally I'd like to know the packing size in advance as I'm doing the job afloat and want to work as quick as I can. Thank you in advance.