I cannot tell you with any precision and I only have a few IPL's to work from, but the earliest models with the iron bore were typically all yellow, later models in yellow and black were typically the 125C versions. All of the parts are pretty interchangeable so there is no guarantee the saw you may look at has original parts...
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The last saws, probably from 1975 onward would have had the OPL and a chain brake option, McCulloch started putting a brake on every saw in 1975 (at least that how they advertised it), most of the operators took the brake mechanism off.
1971 IPL lists the model 600076 and Serial 10-, iron bore
1977 IPL lists multiple model and serial numbers (including 600076 10-...) but these are all chrome bore. Both chain brake and non chain brake are shown in the IPL.
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Mark