Over at Lens Rentals, they've done an absolutely fascinating look at the insides of three popular full frame normal zooms, the Canon 24-70 f/2.8 Mk II, the Nikon 24-70 f/2.8 AF-S, and the Tamron 24-70 f/2.8 Di VC. Something that hasn't struck me until know is how similar the Tamron's lens layout is similar to Canon's. Nonetheless, the elements are mounted in a similar fashion between the Nikon and the Tamron. The Canon, however is more modular in construction, and appears to come apart easier.
Have a look, it's great stuff.