Hey Mike,
Boss 429 had a "quench Hemi" combustion chamber. It's hemispherical but has the two sides near the spark plug and opposite it, squared off. This was done they say to provide slightly better bottom and midrange torque.
The 427 SOHC is a true hemispherical combustion chamber.
They guy I bought my 427 side oiler from had both of these rare motors in his shop, needless to say it was sort of a religious experience for me
Chuck