Need to find a compatible ac adapter
It's my (fairly uninformed) understanding that it's okay for the adapter's current to be higher than the device's.


That is true. The adapter rating is the maximum current it is can supply. It will work quite happily with lower current loads.


  Would the amazon adapter be safe to use?


Yes, if the voltage matches what the pedal requires - 16V AC.

I assume it is well-made and meets all local regulations. Not everything sold on Amazon is.




  the plug as being 2.1mm. I'm not sure if that's compatible


That is a very common standard. Unfortunately the problem with standards is that there are so many to choose from.

It is actually not hard to change the connector with a wire-cutter and soldering iron. You can buy or make adapters quite easily. Parts are available from lots of places (eBay, Amazon, electrical distribution businesses, hobby-electronics online stores, ...) For a 16V AC supply, there should not be any safety concern in making these sort of changes at the low-voltage end.