Online resources are a bit slim for the kind of internal detail which you desire
PT Boats.org does list copies of the original ELCO blueprints in their catalog. http://www.ptboats.org/pdfs/BP-List.pdf
They are exactly what you will need - but will tend to get expensive.
Some of these have been reproduced in smaller format in Victor Chun's book 'American PT Boats in WWII' . They are smaller, and all the information you may need are not there. The popular-press books do not cover the kind of internal details you seek.
BTW -- the aftermarket resin Packard engines sold for aircraft models are not directly applicable for those used on PT boats.
You must really see the White Ensign photoetched detail set for the PT-109. Many of the clunky details from the Revell kit are replaced with this kit. They also make a mor accurate 37mm anti-tank gun which the PT-109 carried at the time of her loss. Much better than the Hasegawa gun which has been used by may others previously.
Colors - basically semigloss white interior and a locally brewed MTB green over a Copperoid bottom. White Ensign makes the correct green. Copperoid was a redish/orange primer-like color