You didn't specify a year, but all small 55.2-60 GMC trucks use these per the 1960 GMC Master Parts Book with no reference to a specific engine. Further inspection of the MPB shows that the fitting on the carb is for 5/16" tubing, so tank to pump would be 1/4" and pump to carb would be 5/16".
Sorry, it's 1951 451. Thanks
