We need to remember that Mopar Performance casting numbers do not tell the whole story. One casting number was machined several different ways, resulting in several different part numbers. Further complicating this, many parts were machined and sold under a part number that was never stamped into that part, and occasionally one part number would be assigned that matched the casting number.
Does this block have Magnum style engine mount bosses cast in? How about Magnum crank sensor bosses? Siamese bores or water jackets?
Based on the photos and description so far, I think this block predates the Magnum race block, the 340 resto block, and the actual R3 series race blocks. I have a printed copy of the spec sheet for those blocks that would come with them, and this casting number is not listed. I cannot post the casting and part number chart tonight because my phone is a dinosaur. Sorry for the excessively long winded post.
