Different types of mcintosh MC240s?

I have for years been using a Mcintosh MC240 tube amp I received from my grandfather, a serious audiophile. Although it makes me absolutely sick to let it go, I am looking at having to sell it for personal reasons.

However, I'm a bit confused.... my amp looks very different from the ones I have seen on here and other websites. For reference, my amp looks like this: http://www.diytube.com/phpBB2/viewtopic.php?t=5368&sid=90837e24c9f20156f0695ef89f798633 rather than the more commonly seen configuration, which is this http://www.auctiva.com/hostedimages/showimage.aspx?gid=1628046&image=576147839&images=576147665,576147697,576147725,576147757,576147805,576147839,576148183,576148250,576148282,576148314,576148347,57614

Does anyone know what exactly the difference between the two is? Is one a higher end model, or is it simply that the configuration changed over time? I want to be as well informed as possible before I decide whether or not to sell it!
Looks like on of them (yours) has a second socket for a 600 ohm balanced line out or to drive a 70v line (70v output is a way to drive many speakers (ceiling speakers or PA i.e. public address speakers without having to worry about speaker impedance). I imagine this was an option/upgrade- whether it is worth more or not I have no idea.