From what I read, this block is siamese bore and can be bored to 4.220. You would want to sonic check it though. I believe the magnum designation means it has the tops of the lifter bores machined for the lifter links and the spider tray. It may or may not have oiling through the block for the shaft rocker setup. I also read that it needs a 318/340 oil pan, not a magnum318/360 oil pan.