I cannot shed any light on the engines used in CN trucks but here is what the photos tell me:
it has been repainted in the present blue color as evidenced by the overspray on the frame. The cab bottom and corners rusting is a common site on these older GM trucks.(AD & TF series)
The dump body is not original to this trucks because it is too long for the WB. Even proper mounting of it wouldn't close the distance enough to make it work properly. There appears to be frame under the rear past the spring ends which is where it would be cut off normally. Looks like a pretty good project truck and should be a lot of fun.
Thank you Moneypit. All of this info is great.. Any yes, it does look like a good project. Wish me luck...