I am making 40hp more than the rated 375hp 440 with a stock bottom end. 275,000 mile stock cast pistons, 8.5-1, reringed with a top fuel hone. I ported the bowl after I had the valves replaced with the larger size stainless. Heads are 915 castings. I couldn't belive how good it ran. I just took parts I had laying around the garage and put a motor together. I was getting married and money was tight.
906, and 915 are pretty good heads, 452's are ok.
I think the 426 heads are better than 906 and 915. I hope you didn't port those.
Brian