We're using AP 8.1A (070919)

We have several different bank accounts with unique cheque specifications. Is there a way to make one of these the default specification that appears when you print/post cheques?

Yes. If you edit the Bank, there is a 'Specifications' tab from which you can assign a particular check specification for printing checks. You also have the choice of choosing different specifications if you print checks from a manual check batch versus generating checks from the Print/Post Checks and Advices section ('system checks').

Duh! How could I not think about checking the bank menu...
Thanks, problem solved!