At least 50% of everything I make these days is of this type. 3 things- imaculate precision fits, guide pins, and a finely finished tang area. The tang must taper evenly from guard to threads (I check it with caliper or mic). The glass rifle bedding compound is best, but I have gotten away with expoy. Get everything on the knife precision fit, finish that tang out nice and then grease it (use a marine lube grease, NEVER vaseline), thicker greases work better than real loose ones. Fill the handle with epoxy or compound and then assemble the knife. Since everything should be very close to final finish, you will want to wipe everything down real well and clean up any of the cementing substance that you can find. Now leave it alone until it is completely set. Doubting yourself and messing with it before it has set will only reduce the precision of the handle fit. If all went right, a slight tap with a wood block on the gurd should break the handle free. Then clean up all the grease.
You will also have to come up with all kinds of cleaver ways to fasten the whole thing together (the nut on or in the pommel). On working knives I use a hex socket bolt (allen wrench type) with a special threaded sleeve mounted on the inside, with the head of the bolt recessed into the pommel. On decorative art pices I make special shapes that can be locked onto with a custom made wrench or pins.