And good luck with the stage III porting. I had a set of 906's done using the MPP templates. They leaked in 5/8 cylinders and cost me about 1200 total when it was all sadi and done.... For a stock set of iron heaads. Awsome. Lesson learned.
Remember tho - "stage III" simply means completely worked - entry to chamber. Template work IMO is not even a full stage II. Personally I use my sonic tester in ports that by design need to be larger everywhere... and even with that I've hit water before due to mad core shift which Mopars are famous for. At my best I can get about 265 on a paid tester's bench from most 340/360 iron heads. That's enough to get 500hp with enough camshaft. But getting paid to do that has to be a labor of love for the owner because it's not going to be the cheap way out. I'd prefer (and almost always recommend) use of a modern design aftermarket head.
My point here was you don't need full porting to reach 500hp. So long as the valves open far enough for long enough and none of it's wasted. IQ here likes those big roller cams and you can read about the numbers he gets from them with worked factory iron heads.