Depends on what type of engine and blueprint you are looking for. Packard Merlin V-1650 - Blueprints, Drawings & Documents | AirCorps Library Ross
This site has some Packard Merlin assembly drawing on their free side. Don't know what else is available behind the paywall Packard Merlin V-1650 - Blueprints, Drawings & Documents | AirCorps Library
It would also depend on which mark you want. A Merlin Mk.1 is a very different beast to a 130 series.