I had to move my 302 head today to get into something stored beneath it, so I thought I'd prove my point that all 1939-1960 GMC straight six engines use the same size (1 1/4") freeze plug on the back of the head. My knowledge was strictly book learning as that is what my GMC parts catalogs say.
To quote Gomer Pyle, "Surprise, Surprise, Surprise!"
Pictures are from GMC casting number shown. The 3983 head was used on all 302 engines, 1952-1962.
Proper plug should be a Dorman 555-022.
'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.
