The fuel distribution would be better if you completely divide the Siamese ports.
Tlowe has done it to his Elky, Turbo6 has done it.
There are draw backs to doing this though. It makes the intake port window too small and really restricts the airflow by a large amount. Turbo6 had to increase the boost pressure by (IIRC) 5-10 PSI just to get the same amount of power output as an undivided intake port. Positive side, more even fuel distribution, smother idle, better mileage possibly.
I do not think it is a swirl effect problem, more of a problem of cylinder scavenging, or? Head boss's were already removed on their heads, no swirl around a head boss action going on, just an adherent design flaw of Siamese port heads.
Lump port would not change this problem either.
I do not plan on making a lot of power with my used 250 turbo engine, so I do not plan on dividing the intake ports for now anyways, because I know how much a divider absolutely kills cyl head flow.
Some EFI systems are made to tune individual cylinders, but if you still have a Siamese port head, you will still have uneven fuel distribution problems.
GM might have stopped testing on the EFI Siamese port head in the 80's, maybe that's why they switched to the 12 port head on the newer 250 engine made until 1997.
