I must politely disagree. London Calling is already a masterpiece. Yes it could be edited down to one LP, but I really think that would do a disservice to the album.
Editing it down to one LP would make it a more focused album. A one LP album could actually be taken in several more focused directions (reggae, straight ahead punk rock, etc.) but I think that would take away from the musical awareness and versatility they display on that album.
The Clash, Give 'Em Enough Rope, and London Calling (as well as the numerous singles and EPs issued during that period) really did make them "The Only Band That Matters". They managed to convert the nihilism present in punk rock and convert it into a more productive political awareness.
After that, inter-band squabbling managed to eliminate and dilute the impact their music had. Sandinista is a flawed masterpiece. The sheer length of the album makes it hard to digest.
Wow, that was some passionate Clash writing. I think I need to go lay down!