The two different length versions are mentioned in Crack In The Cosmic Egg. The longer one is closer to 50 minutes (or a bit over?), shorter one is less 5 minutes or so. Sorry, can't check the playing time of my CD because I'm not typing this at home. When I got it a couple of years back I told Alan Freeman of UT the playing time and he confirmed it's the long version, even though the time was different to what he'd previously claimed it was meant to be.
As far as I recall, the extra minutes were at the end of the record, in the humanity now destroyed/primal soup section. It's great to hear the whole thing but even if you have the shorter version you're not missing out too much.