I have to to correct my last statement. The bolt size is M10 X 1.25, which is a standard metric sice. The US bolt head is 15 mm which is very simmelar to 9/16 inch depending on the toleracnes of the tools. We in Europe replace the Detroit Diesel-bolts as far as possible by standard metric nuts and bolts. Its a Detroit Diesel engine, not a GM Engine. Sometime the space available does not allow that.
The 6.2 l Diesel is the first full metric engine built in the US!
Greetings from a Mitsubishi-owner!
Wolf