welcome to the shop DLyne, there are folks here that can fill you in on that
try some
searches , there was a thread that covered it well - they were made by Chev in Canada, which is where most trucks sent to you folks came from - the only real difference is in the badging, so you should be able to visually identify the year comparing it to Chev trucks .... the 1600 was maybe a 2 ton, equivilent to the US 6100
Bill