Chris,
In this case the cat might be wrong . I have JP Pistons catalogue here ( Aussie manufacturer) and they list 27 hp ( should read 28), from 1939-57, for K, M, O, W, TA, 214 with gudgeon pin to crown height of 1.625" and later 214 1957-76 with pin to crown height of 1.812". So looks like you have to watch out for the later 214, post 1957 as it will not fit a 28hp.
As for your recollections of the SB, with 300 engine, just noticed, there were two different pistons, with a variation of about 0.5" , early 1950-56 and later 1957-76