runing out of idea´s on what to improve

Another head porter I've heard great things about is Ryan at Shady Dell. He can get 300cfm out of those Eddy heads. But realistically, if your J heads really are 'fully ported' then they should outflow the Eddy heads out of the box. So I wouldn't bother swapping unless you go ahead and port the Eddy's.

Also, don't forget that when switching from iron heads to aluminum you want to icrease the compression ratio at least one point. This makes up for the heat loss in the combustion chamber.