[NeighborsComplaint]

If advancing the cam didn't make a night and day difference, then you have created an engine with "lazy port flow due to small displacement, huge intake runners and ports. In a high winding small block Chevy, steep rear gears offset the loss of low-end torque by getting the engine into the power band faster and utilizing the engine's higher RPM power potential (6500-7,000RPM).

This "Chevy Pattern" doesn't work on a Pontiac 350 which shares same stroke as the 400/455. The 455's displacement results in better volumetric efficiency at lower RPM due to displacement but is RPM-limited even with forged internals. The 350 displacement has lower volumetric efficiency despite the longer stroke and the same long stroke RPM limitations. Adding large cross-sectional intake runners and bigger ports results in lazy port flow and loss of power production at low to mid-range RPMs further exacerbated by increased camshaft overlap. In effect, you have created a 450HP capable Chevy Small-block with a 5,000RPM redline. The low end power loss isn't offset by upper register power production due to the RPM limitations.

My gut says go "back" to a stock or Performer intake, #48 /#18 heads and an #067 /#068 cam combination transfer the intake and heads you have to a 400 shortblock for better torque production and resulting street performance.