Sm Blk heads

My flow bench showed only about a 10cfm edge over the LA heads, stock to stock.
LA's are king in the realm of stability, the Magnums have a nicer short side radius and a nicer bowl.
The RHS versions are even nicer in this area.
Conversely, the LA Short Side Radius' are plagued with that dumb angle next to the long wall side of the port that is very close to water. The opposite is true on the Mag, in fact, that funky cavity on the Turn Wall is better for flow but, unnecessarily big in that area, IMO.
Magnum Exh ports are much better than the LA's with the exception of the later LA #596 exh.
The push rod pinch on both designs have their own problems.
Magnum chambers are much more efficient than the LA's. The fact that a Mag head motor don't need as much Ign lead bares this out.
I did a mild set of RHS's that sent a fairly mild 400+" SB that ran 10.33 @ 131 with only 30* of timing in it, on it's first outing. It later went 10.14 @ 133. That's the chamber at work.
The main problem I have with the Mag chambers is, they have much more Int valve shrouding than the LA's, which is a problem with large valves. There is just no way getting around it.
Both head are heavy.
I do not intend to toss the LA heads under the bus.. They have made car's haul for years, including mine.

The LA's hold their edge in valve train stability. Very important in high rpm/high spring pressure situations. Shaft stands are too high for optimum geometry. (.050)
LA chambers do not limit valve size but, while the Short Side Radius being so close to water, you still have some limitations.
The Mag head sports a very good chamber but, is limited in valve size. Funky port, but has good valve coefficient numbers. Terrible valvetrain arrangement, not stable. Too much deflection.
Not racing? none of this matters..