I recently picked one of these up from Goodwill for about $4 and I'd love to take advantage of the built in speech synthesis. At first glance it seems like the expansion port is my best bet to do this, as this adds extra speech capabilities to the Computron. Decoding the protocol blindly is turning out to be harder than I thought it would be, although I can affect the output by using jumper wires to connect various ROM/Expansion pins together. The ROM chip is covered by a blob of epoxy, so unless anyone has an easy way of removing that I think I'm out of luck.
I'd love to get some meaningful results out of this project and I'll let you all know if I figure anything out!