If that block were in use at any point in its history without cats than you can omit them, otherwise you'll need them for registration.

On the NYS DMV form it says something like model year of engine - it's what you put there that determines the emissions equipment expected to be in place. If the 97 block started life without cats you'd be good to specify the first year used and have the equipment as of that point.

Repeating myself but hopefully that's clear?