>I'm looking over the datasheet here and it isn't blatantly obvious
>which 4 pins the 40-pin chip is missing.

If you look at the pinout diagram of the 44 pin chip, you will probably find 
that it is all the ones labelled NC - i.e. No Connect.

The pin numbers for the two functional pins on the two chips probably 
varies, that is you cannot use the same symbol in a schematic and expect to 
get the correct connections for both package styles. 

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