Revert to a previous version of iBooks

I have an iPad1 (iOS 5.1.1, _not_ jailbroken) used mainly for reading books. Just after upgrading to iBooks 3, the app consistently crashes. It might be iPad's low memory as the crash reports are named (tellingly) LowMemory-2012-10-24-221538.log, etc.

Last version of app iBooks 2 worked fine (at least with the sort of books I use in there); also the number of titles is around just 50 and still 9 GB free space. This issue does not appear to be fixable (if it is lack of memory and generaly lower specs), Apple even decided to keep iPad1 out of iOS 6 iteration because of its lower specs, I am afraid the same is true for iBooks 3 on iPad1.

Would it be possible to downgrade to a (previous working) version?

Is there a repository with previous versions of iBooks (in particular iBooks 2)?

I would also appreciate some some guidance on rebuilding the iBooks collections on an iPad1?

(Though, in my case, I could rebuild them manually with some ease, others might find it helpful a proper approach)

(By the way I use other eBook readers -Good Reader is one- but still I would like to have iBooks usability for my purchases.)

Any ideas anyone? iPad 1 is still a fine piece to use.

Enaid