I created two transparent playfields one with gridding set to 30@300 the other set to 300@30. Then placed and resized rectangles within the playfield. The created a simple "Multiply" script to move the one playfield to the left (I changed the forward direction to move left, try it, it won't rotate, there is another method, like most things ;) until it overlapped the first playfield.
I have been spending too much time in Etoys trying to do things, rather than simply think about what I want to do, then figure out how to realize it in Etoys. I hope to spend the next few days looking at other manipulatives and thinking about how to design my own, so that they are simple and fun for teachers and kids.
I also need to think more about fractions and the operations using fractions. If I find time I will head to Rutgers to check out the Robert B. Davis archives.