The bright side is that the PAL16L8 doesn't include any internal state, so it's straight-forward to extract the function tables.
The down side is that I said "straight-forward", not "easy". At the very least, you'll have to get a good connectivity listing (pin X goes to pin Y), and it
might be possible to guess the rest.
It is far more likely that you'll need to remove the part, and manually try every combination of inputs to see what the output is.
http://www.retro.co.za/ccc/mac/ReverseE ... /PALs.html is a good description (in English) of this process, as applied to the Macintosh Plus.