Not real happy about this one, but it is necessary if I am to run the dredger engine in public, at club meetings etc.
The original dredger engine had 3 taps to check on the boiler water levels, like this.
Unfortunately that setup is unacceptable for boiler certification, so I have installed a sight glass using the same penetrations.
The sight glass is a bit short, but it should comply with the regulations.
I have spent another half day experimenting with different spring configurations, so that the safety valve releases at 40-50psi. Eventually I decreased the coil pitch of the spring, and the valve now releases at 45-50psi. That will do.