I installed a 3:55 ring and pinion in a Canadian differential and can share the following:
The bolt hole circle ( tapped holes) on the new ring gear was 6.062" diameter which I assume is the same for all U.S. trucks. The Canadian ring gear had a bolt circle of 6.188" dia. (thru holes). To make things fit the holes (and spotfaces) on the Canadian carrier need to be elongated 1/16" radially towards center or 1/8" on diameter. This is the only modification required.
