Most of the Ford Racing GT-40 crate engines come without intake for this very reason (because Ford Racing is leaving it open to whether you want to run a carb or fuel injection, and whether you are running a street or track intake, etc.), so you can just buy a carb intake and carburetor and bolt them on and go.
The second part of your question, about building a cheaper 300 horse motor, can be answered in a thousand different ways. If you want some ideas, try checking out the websites for some Ford magazines and checking out their performance street engine build-ups for ideas.
Try FordMuscle, Mustang & Fords, 5.0 Mustang and Super Fords, Muscle Mustangs & Fast Fords, etc, etc. Once on their respective sites, do searches for what you're looking for. There are tons of documented builds on reliable small block ford street engines that put out 300 horsepower that you can sift through.
