The 5.0L is small, light, cheap, easy to find, and makes decent power. Car Craft took a stock short block from a HO Mustang, used headers, a set of AFR Heads, and some ratio roller rockers and made just over 400 HP with 9.0:1 compression at like 6500 RPM. Not bad, cheap, plenty of power and even lighter with the aluminum heads.
My car is almost driving, Im using a T5 manual, a HO 302, EFI and it all fits under my hood. I bought a new wiring harness for the engine for less than 500 after shipping from fordfuelinjection.com and its really nice, plug-n-play. After I get a new job I will be replacing the engine with an aluminum block/head 5.0L and a Tremec TKO/600 transmission. Its the only way to go