HYDRAULIC FLAT TAPPET: For 9:1 to 10:1 compression. 383 needs 2500 stall. 440 needs 2000+ stall. Use 700-800 CFM carburetor, headers, 3.91+ gear.

"The miss doesn't go away when I rev the motor and it seems to be getting worse over time. There's always been a slight miss that's now getting worse."
Do a leak down test, that will tell if any valves are hanging open.
You'll also need a timing set that has the ability to be degreed. I would check to be sure the cam didn't wipe during break in.