Picture below is of the cylinder 6 of the 2193983 head that came to me on my military 302. That casting number was also used on 302 engines from 1952-62.
The fitting with the green tape on it is where the "bypassed" coolant leaves the head and travels through a metal tube to the bottom side of the thermostat housing. The "boss" (hope that's the right word) in the head for the fitting is in all the GMC heads that I've seen (even my 228), but is is not drilled and tapped for the fitting.
'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.
