After a bit more research.
Up to 1985 trucks were badged 'IH' in the centre under the windshield with 'International' on or above the grill. Also some cab handles had the 'IH' logo.
So I guess 'International Harvester' can be used as the makers name.
After 1986. Navistar International Corporation became the holding company for 'International Truck and Engine Corporation', manufacturing diesel engines, trucks, and parts under the 'International' brand.
So use International as the makers name for trucks.
From 2002, 'IC Corporation', a wholly owned subsidiary of Navistar International Corporation, produces school buses as the 'IC' brand of buses.
So use 'IC' as the makers name for buses after 2002 (International between 1986 and 2001). 'IC' website...
http://www.ic-corp.com/site_layout/index.asp
I can find no mention of 'International Navistar' for armored trucks on corporation websites other than dealer/sales websites. But as a specific range or trucks I have no problem with identifying them either way.
After 1985 Case or CNH became the owners of the following brands and logos, 'IH', 'IH' Logo,'IH-HARVESTER', 'IH-INTERNATIONAL HARVESTER', 'INTERNATIONAL-HARVESTER'.