I've noticed a similarity between the red finned exhaust of the Project sword BOOSTER ROCKET and the grey finned heat shield (?) in the centre of the JR21 THUNDERBIRD 3 as ringed in red above. Did JR21/ Century 21 simply re-use/re-tool this part? If anyone has the TB3 and the Booster Rocket and can send a piccy of them stood together we could see if the two finned features are the same size and shape.
Pictures: Woodsy and unknown Internet.