Hank, yes it was naturally aspirated. At that time, his engine made the most HP per cubic inch(2.14 HP/CI) of any N/A inline in professional competition at 535HP out of just 250 CID. The intake ports were in no way stock in size, it was a full tilt 320+ CFM head from Sissell from his peak time in his career, prior to his passing. So if you can picture the head Kirby has of ours that you've mentioned before, just think of the floor being ground out to the point of it being before you put the brass in it, and stick in a divider full depth. I know a racer currently that I have been trying to get some pics from, that is using this same technique, but has welded the divider in place. Of course, nothing is easy, you have to open to ports up, and im sure they are doing other trick things, but he is being vague in some areas, because it is still kinda' secretive to most of them that use it. But from what Darren told me he did 10 years ago, it ain't rocket science if he did it. He just took some tin snips and formed some dividers to tack weld to his header flange, and he saw a pretty big gain from doing just that. But like anything else, some amount of tweaking or R&D, might be needed to evaluate fully the best overall shape or style to make the dividers and ports.
But don't anyone get ahead of me here. I have always been Pro-lumps, either bolt-in or weld-in, because I have a pretty long background with that technology. But if you want to know what works, just look at what the top guy's are running and setting records with right now. There must be something to it, or they wouldn't be doing it, because they race to win, and if it doesn't win, they don't use it. If I can get some pics, i'll gladly put them on here so we all can give it a try.
