Split/reformat text file
 

I have a mainframe print file for 2-up checks. I converted it to a text file with the control characters removed. How can I easily split the side by side checks to print 1 per page on a laser printer. The checks are numbered, so they need to print 'left, right, left, right.... etc'. Any thoughts for easy conversion?

ex.: Check1 Check2
Check3 Check4

Output needed: Check1
Check2
Check3
Check4