The Poly chamber and valve arrangement was marginally better for combustion efficiency and flow compared to conventional wedge heads but that was easily made up for by increasing the compression ratio. According to my "Chrysler Engines: 1922-1998" book by Willem Weertman the LA was a revision on the A-engine to reduce weight and width so they could offer a small V8 for the new (at the time) A-body cars. Somebody on here once tried to argue that the "L" did NOT stand for Lightweight but in this book written by the head engine engineer at Chrysler at the time that's exactly how he describes it, "Lightweight A". I believe they were able to shave 50 lbs off the A-engine while still keeping the heads and intake manifold cast iron.
Also because of the wedge head they were able to take advantage of quench/squish and run higher compression ratios, at least on the early LA engines with closed-chamber heads. My big question is why they dropped closed-chamber heads for LA engines after 1967(?) and never bothered trying them again until the 1985 318 roller-cam engine. Literally since the beginning of Chrysler Corp they were pioneers in making flathead engines with "high-turbulence combustion chambers" which was a quench pad. They knew its benefits back in the 1920s so why toss it out? Unfortunately it's not mentioned in the book in the chapters about our beloved V8s...
