Brief:
Converted an Estes Monarch to a 24mm x 95mm motor mount.

Modifications:
The need for SPEED: Leave out the motor tube, aft CR, and engine hook. Use an old E9 engine to set the remaining CR 3.7 inches from the back of the body tube. This CR is now the motor mount.

Construction:
You may want to use thin CA to harden the aft part of the body tube so it can deal with the abuse of having to have engines repeatedly inserted.

Flight:
RockSim shows it is 1.6 diameters stable or greater on Estes D12s through Aerotech F21s.

It flew on D12s straight and true with streamer recovery to get it back down.

It simulates to 1600ft, 50% greater than with a C6-7.

If you feel lucky, try a E15, which sims to 3000ft. An E30 goes just under Mach 1 with almost 70Gs of acceleration. An F21-8 shows 3637ft and a couple of percent shy of Mach, which would probably be a shred zone but spectacular to see. Just don't use a 24/40 case if you want to keep it.

Summary:
Goes up great for a minimum diameter rocket. Just get out your binoculars.