Thanks for the update.
Here's the simple skinny on Chiefs Special Models 36 & 36-1.
Model 36, 2" or 3" lightweight barrel, round or square butt, blue or nickel. (Model 36 3" lightweight barrel discontinued in 1976.) Model 36 2" replaced in 1988/89 by the Model 36-2 2".
Model 36-1, 3" Heavy Barrel, round or square butt, blue or nickel. (New model number; NOT an engineering change. Made concurrently with the Model 36. First ones we know of--serial numbers 456070, 456176, & 456212--shipped in September 1966.) Model 36-1 3" Heavy Barrel replaced in 1988/89 by the Model 36-3 3" Heavy Barrel.