It's a joyful place with so much old technology yet a refreshingly hands on attitude. I don't think there was a single exhibit that wasn't interactive by one method or another - which really matters when you're talking about technology that is largely at an age where kids are too young to have grown up with so it gives them a chance to play with the predecessors to their much loved consumer hardware - and it gives us adults a chance to do more than just reminisce about the fun days experimenting with emerging technologies.
I'd highly recommend that museum on it's own merit; let alone spending the day exploring the site and Bletchly Park as well.
They're currently located in an industrial estate in Cambridge, I'm sure if/when they move they will get much more attention.
Are metallic delay lines sufficiently similar to mercury tanks that it's not an architectural issue to switch them?
As to architectural properties, the main thing that they want out of them is that they delay signals by the same number of microseconds; arranging that is not a problem.
The computing museum is also interesting; BTW, in addition to the Colossus rebuild, they're also constructing a working EDSAC replica (using metallic delay lines instead of mercury tanks for memory, but otherwise as exact as possible), and have a bunch of other interesting old machines in the collection. For visit planning, though, it's open fewer days than the Trust-managed property.