Bullit34, to ID your heads, note the locations of the relevant numbers in this picture then go look at your heads:
If your heads are original '74 455 heads (not sure what casting number that would be), then your compression is a dismally low 7.8:1 or thereabouts. Time for a head swap. The 6X castings in the above picture would be a good choice, as would several other castings from mid '70s 350 and 400 engines, such as 4X and 5C. '71 #96 would also be good, as would '72 #7K3, but those don't have the end bolt holes for the headers.
That tiny carb is hurting you. A 455 is a big engine, it needs a big carb. Think 750 cfm or bigger.
You mention a "mild" cam. How mild? Anything less than 220 @ .050" duration is throwing away most of your engine's potential.
Good luck!