Actually the Heavy Half was GMC & the Big 10 was Chevy. Modern day recreations are becoming popular.
The 1979 model year F44 package included a choice of 1,625 or 1,700 lb front springs (1,475 and 1,550 lb front springs were commonly used on standard C10/C15’s), 2,000 lb capacity rear springs (1,550 lb rear springs were standard on regular C10/C15’s), heavy duty power brakes (manual and light duty power brakes with smaller rear drums were offered only on standard C10/C15’s), larger tires in a choice of 1,790 and 1,905 lb capacities (several smaller capacities were also listed for regular C10/C15’s) and the 305 V8 (the 250 six was standard on regular C10/C15’s). With the exception of the 1,700 lb front springs, all of the F44 components shown above could be ordered separately on the regular C10/C15. Depending upon the equipment selected, the regular C10/C15 offered GVWR’s of 4,900, 5,300, 5,400, and 5,600 lbs. However, by selecting the F44 package, the buyer received all of the above equipment, plus the bodyside decal designating the C10/C15 as a Big 10/Heavy Half, offering GVWR’s of either 6,050 or 6,200 lbs (depending upon the tire and front spring capacities selected). (You can determine your Big 10’s rating by checking the label affixed to the driver’s door frame.)A few other notables should be mentioned. For 1979, the U.S. EPA established fuel economy standards for trucks up to 6,000 lb GVW. To meet these standards, GM equipped the standard C10/C15 with a special hood seal and underbody air dam, and also offered a selection of rear axle ratios biased in favor of economy. The Big 10/Heavy Half GVWR’s exceeded the EPA’s 6,000 lb threshold, and accordingly, those models were not equipped with the hood seal and air dam. Also, the F44 package allowed the purchase of lower axle ratios, and the 454 V8 engine option. In contrast, the 350 was the largest engine available on the regular C10/C15. Prior to 1979, the EPA considered all trucks under 6,000 lbs GVW to be light duty emission class vehicles. With few exceptions, these vehicles required undesirable catalytic converters and the use of unleaded gasoline. The F44 option was introduced to allow buyers the possibility of buying a heavier duty ½ ton truck that could use cheaper leaded gasoline. However, for the 1979 model year, the EPA expanded the light duty classification to include all trucks up to 8,500 lbs GVW. Thus, the Big 10/Heavy Half (and all ¾ ton Chevy C20/GMC C25 trucks, as well) lost this particular advantage. Only 1 ton C30/C35 series remained exempt from catalytic converters and unleaded gas.Excepting the differences discussed above, the Big 10/Heavy Half was identical to the standard C10/C15. A 3.14 section modulus frame, 3,750 lb rear axle, and 15 inch wheels were common to both. These components were much more robust in the ¾ (20 series) and 1 ton (30 series) models