Big block a-body k-frame

Here are 2 additional photos to try and clarify any misconceptions about this part.
According to http://www.engine-swaps.com/Pages/ProductsType/K-Frames.html it is an a-body big block spool mount k frame because the measurement inside the perches measures 3 3/4 inches across.
Furthermore, I know this for a fact because this k member was in a duster with a 440 before.