What carb was this intake ported for? Have any ideas? Is done really well. But I'm just going to open the entire top and hopefully get this hvh spacer. Good or bad idea to open the top of the intake uniformly all the way around?
The odd shape is for a Thermoquad or Holley Spreadbore. Don't worry about reshaping the plenum for your build. Just bolt the spacer and your carburetor right down.
If one was to modify the plenum, you would weld it up and reshape it for the 4150 style carburetor.