Okay I took it apart. The first picture shows the assembly from the point of view of the lamp. You can see cracked piece of HA glass still in place. The second shows one half of the assembly, normally two bolts hold it together. The HA glass slot measures 2.5mm the dichro glass slot is about 1mm. The third picture shows the other side with the dichro glass in place. The fourth picture shows a piece of HA glass 33.5mm in dia that I pulled from an Omega C760 Dichro head - it sort of fits on top maybe a couple clips could be fashioned to hold it there. The last it a group shot. The C760 glass is 2mm thick. It almost could be made to fit but I'm not sure if it's tempered. From what I have read tempered glass is very difficult to cut and cutting/shaping destroys the temper near the edges. Maybe someone who knows glass can comment on the cracks in the rectangular piece and whether they indicate tempering.
I don't know if this helps much, but if you need any measurements it's living in a box on my desk right now.