Hi Norman,
I rebuilt an example of the kit about 8 years ago, having been presented with a model in a similar state to yours. I did not have the original plan but obtained a copy of John Haynes drawing from him at the time. I suspect it shows a lot more detail than the original kit plan but I don't know if it is still available from him. At the time he did his own Elco PT boat kit and also supplied me with lots of detail parts including the guns.
I wrote an article on the rebuild for Model Boats magazine which was published in September 2010. It is still available on the Forum if you are a subscriber and search under PT 602. There is lots of information on the web about Elco 80 foot PT boats – Google is your friendly assistant.
Here is a photo of the completed model

Gareth