Unless Canadian rigs have a different numbering sequence, the displacement of the GMC engines will be included in the stamped (not cast) number on a machined pad beside the distributor. 228, 248, 256, 270, 302, etc. The 256 was used in some WW II era Canadian military vehicles- - - -very scarce down south! I have bore and stroke information and engine bearing specifications in a couple of old Federal-Mogul shop specification catalogs. There are a couple of other Stovebolters who are very well versed in GMC-speak, also!
Jerry
