Nah, I don't have anything else I need to work on. I'm taking a break from my own cosplay and props and what-not, but I do definitely want to help you out with the massive key (does it have a name, by the way? I'm just curious).
I am still thinking it out, but I'd say for the main bulk of it use a large pvc pipe, and......hmm....you could carve and shape wedge out of craft foam/polystyrene then take plastic sheeting and wrap it around the pipe and gluing it to the craft foam wedge. This way, it would leave a tunnel for the pipe to slide into, and then you'd have the ridged key end. heh, I'm not explaining this that well but I can explain it better next time I see you, lol. I've got some plans though.