Congrats

 

HEMI refers to the shape of the top of the combustion chamber. It is is hemispherical or "half of a circle", or "domed" would be a better way to describe it. The design itself was first used in aircraft engines in WWII. The design was created to improve volumetric efficiency to increase engine performance. It was designed to outperform Japanese Zero's that were using nitrous oxide at that time to gain the performance edge on our outdated "pre-hemi" warplanes.

You can change the heads or the block, but if the heads remained dome shaped it is still a Hemi.