CDN 6cyl GMC's had Chev engines, otherwise they are all GMC, and the frame, suspension and details [dash, grill, trim, options] are
not any more Chevy than the US GMC's are, and the V8's were not 283's
Photo - yer truck's vin indicates a 9314 series/model, which is a short 1/2T with a 5000GVW - if you've got a 9' box and tags that say 7000GVW, someone has done a switcheroo on the vin tag

the long [133"WB] 6,900/8,800GVW pu is model 9434 - wheel sizes make the difference in GVW - also the 8 [79314
809605] in the vin indicates a V8, a 235 would have a 6 instead
Bill