I was loooking through a 5.0 magazine on the plane today and I saw one place advertising a 5.0 GT-40 Explorer crate engine for like $2k. What's the difference in hp form that to say a garden variety 5.0 from a stang? I thought I heard that they just have a different cam or something but already had the GT-40 heads.

check out this link:
http://www.fordracing.com/performanceparts/html/PartDesc.asp?PartType=&VehicleType=&PartNumber=M%2D6007%2DP52%2A

there is a whole list of engines at http://www.fordracing.com/performanceparts/
click on "part search" and then click on "engine assembly"