Jon,
That F150 would be a great doner for the engine!
In Cobra's, just like everything else, "you get what you pay for". Personally, after spending more than 20 years building and upgrading my car, I would recommend buying a second hand car. There's some pretty good deals out there. Most Cobra's don't have many miles on them. Takes a certain type of individual to actually drive these cars and live to tell about it.
Are you man enough?
Paul