I had emailed Tim Robinson who's been working on Meccano versions of the Analytical Engine and Difference Engine. He graciously replied:
My website is quite out of date and I have done a bit more since I last updated it. I have a new and much better version of the control mechanism (operation cards & barrel) which is much more reliable than the one described on the website, though still probably not good enough for a real engine. It also incorporates a critical feature which was missing from the first version (the ability to branch at the last moment on a result generated in the current cycle.).
I have a working demonstration of an anticipating carriage on 12 digit numbers.
My current project is a store, but I have a long way to go. The sheer quantity of stuff needed to build this is one big problem, together with the tedium of making huge numbers of identical assemblies.
I'm sure you have realized that the biggest single problem in proposing to actually build an AE, is deciding exactly what it is!
The initial difficulty in building the engine will be around deciding what constitutes a Babbage AE. The initial approach will involve a research project and computer simulation of the AE hardware. From there the project can continue to the actual physical device.