Are these swirl ports?
Here is my overall assessment of this topic. They are factory cast iron heads. Putting a label on them changes nothing. If you are using them chances are you are not building a race car and top performance is not the goal anyways so why worry about a label ? Imo there are about 4 or 5 different sbm heads you have the early 273 heads them the early open chamber small port 318 heads then there is the early 340 heads with 202 valves then there is the later 340/360 heads with 1.88 valves then you have the later 80s 302 and 308 closed chambered heads that pretty much sums it up. Imo for a street car eith a little work they all are good usable heads and can make decent enough power to have fun with. Obviously they are not going to make the same amount of power as a fully ported race w2 head or a fully ported aftermarket aluminum head but they are good enough for a fun street car.
