Hi Steve. Thanks very much for your input here.

Firstly, I found this tiny (about 5mm long) maker's mark stamped into the horn - "WD Co". This seems to attest to Altec having at least for a time, outsourced the casting work....

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Re your technical observations and advice... I am not even close to having more than a very basic understanding of this stuff.. What I do have is curiosity and some skill with tools and equipment. If there is a better design, more suited to the GPA 902 driver I intend to use in this build, well, I am happy to build it. But someone would have to supply me with plans, because there is no way I could work it out myself at this point.

One of my plans however is to experiment with different horns once I have the 811 copies up and running (along with the rest of the system!), so I am happy to continue as planned with these.

I do appreciate the suggestions - and if you can point me to plans for any horn you deem more suitable, I will gladly take a hard look at them :-)