The refractory set and I successfully stripped out the cardboard mounds. It came out pretty good except for the roof panel, which has cracked a little and is in no way a close enough fit, so will have to be re made.
The interior space is adequate for what I need and it set really hard.
The crack through the roof plate is too big to repair so I will make a new one.
Overall I am very happy with the result and will now start on a larger version and order a burner.