[455Grandville]

The rods are longer also (6.135" vs 6.75) but its still based on the big block Chevy, heres something off the website : (Ive seen both the bare blocks only minor changes the 8100, they probably changed the coolant patterns again !))

The 8100 was borne out of GM Powertrain’s earlier 7400, the familiar and ubiquitous 7.4-liter V-8. The 8100, which displaces 8.1 liters, shares the same bore as the 7400: 4.25 inches. A longer stroke, 4.37 inches compared to 4.00 inches, gives it the added displacement. This is an unusual strategy in high-performance engines, where increasing bore is the preferred method, but GM chose it because a longer stroke typically translates into more torque and better durability.