THAT was my whole point, Einstein. There is NO ROOM for big valves in a slant motor because the bore centers are too close; only 4"... The Chevy small block is 4.4".
That is why they will never run, naturally-aspirated.
Maybe, someday, if somebody designs and produces a 4-valve head for this block, it will have a chance to breathe, but until then, forced induction (or N2O) is the only way...