Thanks--this will be very helpful, especially if my below experiment fails.

The block itself does not bare much load, right? It has to be airtight but that is basically it. As a test, I cast the block from alumilite plastic compount using the cracked original for moulding--that stuff is pretty hard and strong! Machines well too. According to specs, heat resistant to something like 400F. Seems like a good choice. Please let me know if it should not be used for this.