PJ,
The PBY used the Pratt & Whitney R-1830 Twin Wasp radial. Other than sub varients, it's the same engine as the F4F Wildcat, the B-24 and numberous other allied planes used during the war.
For a good twin sound file, look in the archives here and search for "Lawdog" as the author. Get a twin sound pack for the Twinwasp for most authenticity. In the end, you can alias your PBY to your stock Wildcat and you won't be too far from wrong.