Where to start?

I personally don't like mixing brands. IF I had a 40 ford truck, she'd get a ford motor. But, when people do T-buckets, and Roadsters, and the such, put what ya want in it, cause nobody knows what it is anyways. But again, your car, your money, you da boss :D
The easy play would be to be a fox body mustang 5 liter 5 speed and remove the running gear for my 40 pickup build. I have never done things the easy way.
I have not made a decision however, I was just making conversation on someone else's thread, that and a friend has at least 5 318's he will gladly give me one.
After all it is a 40 ford pickup and the only thing I can guarantee you won't go in it is a effen 350 GM product!!