How much fuel pressure and gph is required to support 500-550 hp? The carb is a Holley 780 cfm. Also I'd like to use one that won't present clearance problems.

Mech or Elec ?
I run the an older version of the Holley 110gph.
http://store.summitracing.com/partdetail.asp?CP=1&part=HLY-12-327-13&N=700%200&Ntt=HLY~12~327~11%20or%20HLY~12~327~13%20or%20HLY~ 12~327~20%20or%20HLY~712~327~11&Ntk=&rsview=sku&Ns=P_Rank|0
And I know allot of guys on hear really like the carter version as well.