H1 Engine Replacement w/GM

[GFR]

Have a 1998 H1 6.5 turbo diesel fire truck with a cracked block at only 12,189 miles. Has anyone installed a GM 6.5 turbo diesel instead of the AmGeneral engine and if so, what problems did you encounter. The local Hummer dealers says there are lots of issues and the additional labor is more than the added cost of the AmGeneral engine. People selling GM engines say they just drop in. Any help or experience is appreciated. Thanks, Bill at Genesee Fire, Colorado