Mild 318 misses at 3000rpm

2000 rpm is to fast for your specs. You probably want your total coming all the way in at 2500 plus.
Do you know what mechanical advance is in your distributor?
If stock unit without mods you could have 26 to 30 degrees mechanical advance you are adding 20 initial too. Not good.
I don't know. " Jim I'm a carpenter, not a mechanic!!"
Dizzy is a stock reman off the shelf at Napa for a 74 318
Going to get another i case the pickup is bad. I'll ask if they can tell me what the mechanical advance on it is.
So where would you set initial?