At PRI 2021, I stopped by the Noonan booth and was looking at some of his stuff when I saw a Hemi that looked right, but on second glance, didn't look right, so I asked him why my eyes were playing games with me.
He said the, were not. In fact the engine was based on a 4.500 bore center build model not the usual 4.800 Chrysler bore center model. Before I could ask him why, he began to explain that one of his ProMod customers and apparently a significant contributor to the class (financially) was looking for an advantage.
The advantage they came up with was a rules defined small block that looked (at first glance) like the real McCoy — except on a 4.500 bore center. If I recall correctly, he said, the customer bought ten engines from pan to injectors at $100K each. NHRA apparently pushed back and the competitor threatened to pull back his funding for the class. Out of the clear blue it suddenly became obvious it was a small block and could race at small block weights breaks.
I was impressed because the small block version had the same or very similar porting and valving compared to the big block version of the engine — go figure? It looked as if the porting and valving of the BB version was directly carried over to the SB version. Sort of a Smokey Yunick style upgrade.
I think Smokey famously once said something like, 'The rules just tell you what you can't do. They don't say anything about what you can do ...'
In the FWIW bucket, I just checked Noonan's website and there is no mention of, nor pictures of a 4.5" bore center Hemi block.