They are much stronger blocks that can be compared to the bowtie blocks for Chevy's.... or SVO blocks... for Fords.....
Have 4 bolt caps... big thick main webbing.... hell for stout...
They used them in the Busch series when they were 6 cylinders... and indy cars....
Blocks never came from the factory in any cars.... strictly race engines. They are practically the only alternative when power levels go up over 750 HP.