I don't have any parts, but I do have a GMC Master Parts Book that covers your truck. If I can help with information please let me know. Below shows the GM part numbers for your gasket. Perhaps an internet search using these part numbers would turnup something.
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'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12
'52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.