A 1950 USA GMC 100 came with a 228 engine.
A Canadian 1950 GMC came with a 216 engine.
If your GMC has/had a 216 engine mounted in it, you should be easily able to mount a 235 (or, 261) in it.
You can get a 235 engine to work on a 1950 USA GMC frame - maybe someone will confirm/correct, and explain how/why?