The Scorpion is actually a true 4" kit with a 3" motor mount.
I know, I have the actual rocket described in the thread.
I haven't flown it yet & consider it a collectors piece.
As for Dynacom;
I don't think they're making any more kits.
They did re-open briefly under the name; Air-X https://www.rimworld.com/airx/
The kits are pretty heavy, tipping the scales nearly 20# without motor or parachutes.