I just checked out a 1973 Horizon that has a tunnel/runner hull like this (this is not the boat, just a pic I found of the same bottom)
http://www.clubkustom.com/getsumbaby/boat_rear.jpg
From the posts I found in a search, a few said they tend to porpoise. It has a 454, dual quad tunnel ram w/DPs, Vertex mag, OT headers, and AN E PUMP!
Anyone know how it handles, any quirks, etc?