I put the fins on, and the (square) launch lugs,
and I discovered the v-notches in my Saranac carton may be good for supporting round rockets, but they’re even better for square ones.
Square is relative, though. You can see the body tube isn’t quite square; the sides bow out just a little, and the corners are rounded.The nose cone as supplied, on the other hand, really is square. So you need to take the supplied 80 grit sandpaper and knock down the corners on the shoulder to get it to fit — I had to sand the sides of the shoulders a little too. Now the nose cone fits, but while it lines up fairly well with the body tube in the center of each side, the corners of the nose cone stand proud of the body tube by a good bit.
So those will need some sanding, too, to make the profiles match better.