Whats a good 97 f250 replacement engine?

I am getting a 97 f250 for free soon. I'm 15 and still learning about cars and I'm trying my best to learn. My hopes are to make my truck a "prerunner" or street legal trophy truck like this, http://socalprerunner.com/wordpress/wp-content/themes/thesis_17/custom/rotator/0611or_01_z+custom_ford_f150_prerunner+front_left_side.jpg, but i have no idea on what engine I want to get because I dont know what types (Crate, small block, big block ect) can fit inside it or how much better it is cuz I dont know at the moment what engine is inside my f250 currently but its not a diesel. But what I do want in a engine is it to FLY in off road terrain and I want it to scream like 572 chevy.