I've recently acquired a couple of '27 and a couple of '28 heads and while pondering the differences in them, I got to wondering. Chevrolet surely knew for some time that the new 6-cyl. engine would be coming in 1929. Why do you suppose they went through the time and expense to redesign the 4-cyl head for that single and final year?

That is a good question, maybe the chassis builders (extended radiator and 4 wheel brakes) were ahead of the engine builders, it could have taken longer than they expected to get the new engine road worthy, and probably the dual port head was in development for several years before 1928 and they may have needed to do something "new" in 1928.

Any way it is a good item for research and discussion, it seems to me....

Probably for the same reasons they changed the cylinder block to full water jackets from 1/2 in 35 to 36. The main reason it takes a couple of years to determine what changes are to made in Engineering then a long time to make up models and molds then test them on dyno's and the car test at the GM Proving ground and hot & cold weather tests before it goes into production. I bet it took over three years to do. All the way up until the 90"s it took 4-5 years to bring out a new model. Meanwhile the other car manufactors come out with there changes requiring Chevy to keep up. Todays car builders through their "spy" networks will know what the other car builders are planning for the next 4-5 years.