since pdftk is not smart enough to deal with input files order, replace the last step with:
> FILES=`perl -we 'foreach $i (1..439) {print"cr_$i.pdf "}' | xargs`; pdftk $FILES cat output newbook.pdf
old thread, but for the sake of future googlers with the same problem, if you have pdftk, imagemagick and perl, here's an anwser (modify density and chop arguments as you like):
explode the pages:
> pdftk book.pdf burst
right pages
> perl -we...