Brent,
I use the Holley MPFI on my 521. It has a Torker II manifold which is the least tall I could find for the 460. I use the 1000 CFM throttle body and complete setup - see Jegs/Summit for prices. Even with the Torker I still had to raise the hood scoop about 1-1/2" to get a decent air filter on.
I now use 42 lb injectors into bungs welded into the Torker with Aeromotive pump & filters. Now that my second Aeromotive pump has failed, I think I may try a Walbro. The Aeromotives seem to last 5,000 - 10,000 miles and then burn up. Aeromotive rebuilds them for about $100US but it's still a pain.
Overall the system runs pretty well and I'd not go back to a carb. It does need a laptop and some time to learn the system and how to tune it.
Support is here for the Holley system:
http://www.chevytalk.org/fusionbb/showforum.php?fid/35/
If I haven't discouraged you from using this system, I'll be happy to answer any specific questions you may have.
Tom