That was the original Bandit "T", designed for a JPX turbine. That is a propane tank, just like on your barbecue. It had a 90 degree rotating nose retract to clear the bottom of the tank.
As for the fin mod, keep the little forward locating pin, but add a 4-40 bolt behind it. You need an access hole in the fin leading edge to get a ball driver in to tighten it. You mount a little plywood plate under the fin in the fuse to hold a 4-40 blind nut. You have got to get the fin on there securely especially if you want to fly fast.