The serial numbers are engine numbers. They should still be able to tell what threads are in the the heads for the spark plugs.
I also found a little more in two issues of the Service Man . April 15 ,1929 another set of heads were used on the cars between 4-14348 and 4-17364 (the early metric heads) these had a slightly higher compression than the standard HC head of 5.3. This head was never avalible for replacement.The later HC heads had an"X" below the HC to distingush them and were 5.3 heads.
All this probably doesn't matter. In the Sept 1,1928 issue, where the 328 is introduced they say " THe 328 cylinder heads,blocks,pistons and pins are,therefore ,not interchandeable with 303 parts." It is refering back to a statement that the bore was increased to 3 1/4" . It also shows a picture of a section of the head. Near the bottom directyly below the 53 , they have 328H cast into the head. Warren