Gadget, most people that try doing porting without understanding or proper schooling normally mess things up. The GM-90 head has a J figure casted in the pocket underneath the intake valve. Its roughly 1/4" tall. I agree that it's there to increase air speed and in turn also helps with swirling effect. As I wrote, this would also aid in mixing a gas that's injected in the intake. These engines, including the CS listeroid's dont need large valves or porting. Doing so will reduce air speed and in some instances it will effect performance and efficiency. Now, if there is casting pieces that can break than yes, get it out. But otherwise most of the time it's best to leave it alone.
Brings back memories of the Ford Boss 302 and 351 Cleveland engines. The intake valves and ports were too large for street use. The engines would gas foul the plugs so often. They would not run right until you were over 4000 rpm they ran great over 5000 rpm. This was the reasons why a the Australian Cleavland heads became so popular. Smaller combustion chambers and intake posts. They work great on street performance engines. The Aussie's got it right.
It would be interesting to see that head. Diesel heads typically have zero valve tilt which makes for a horribly bent port but it makes it easy to keep the combustion chamber flat.
If the lister has a volumetric efficiency of say .9 and displacement is 1.434L that puts air flow @650 RPMs at about 15 CFM. So every second your trying to cram in .25 CFM through that tiny port with a volume of say 1/10 that? That give you an idea how fast that air is moving through there.
That gives us about 2.5 CFM per Horse power. That is plenty of air in theory. Problem is, I doubt we are seeing .9 volumetric efficiencies, from the looks at these ports, I would guess more like .6 - .7 at best. Thats assuming correct valve timing.
That could be why listers can smoke a bit even though technically they should have enough air at heavy loads. So....in theory, if you can get a bit more air in there, you should see less or no smoke under full load and better economy under heavy/full load.
But how many of us are running under full load all the time? I'm guessing no one.