I seriously doubt you could stuff one of them in an HD without serious firewall mods. If you look at the HD and HR, they have a flat firewall, with no indentation to accommodate the engine. Part of the reason why this is so, and a contributor to the massive plough understeer of a stock HD, was that GM moved the engine forward 3 inches from the EH, to lower the transmission hump. Look at an EH and HD crossmember, the engine mounts are at the rear on an EH and the front on the HD. The free space front and rear in the HD engine bay isn't great. An Ecotec would fit easily. A Barra? Nah.