Hi, HerrPhy,
I have compared the pin assignment for the 11U34FBD48/421, 11U35FBD48/401 and LPC11U24FBD48/401, I think the pin assignment are the same, pls check again yourself.
Regarding the "binary code compatible" question, I am sure all of them are binary code compatible, because they use the same core ARM Cortex-M0.
Hope it can help you
BR
XiangJun rong