Major upgrades! Any ideas on hp gains?

I forgot to say I have a "mild cam" already, but yes I do understand that the intake will still be restricting me pretty badly. I have a 904 so I am going to stick with a dual plane manifold. I have not decided which one Ill be running yet. Ill be driving this on the street mainly. I say "mild" because I know when I built it 10 years ago I sat down with a knowledgeable guy and figured what i needed based on what it was going to be used for. So I remember its not stock, but I had the J heads in mind when Building it. As for the carb I have a 1405 Ed, i think that is a 500/600 cfm carb. If I have to go bigger there Ill do so. Thx guys