Jumping back to my 555, I should had mentioned the exhaust had rotted out when I got it. A Danarm 55 stack fitted perfectly, even behind the long brake cover. this gives some idea how close the Danarm 55 is to the 10 series.
Moving on to large frame saws, I have never seen a MccCulloch gear drive in any form show up over here, nor a 125.
I have a few 250 Supers, a later USA built black top and several early Canadian built yellow tops.
The Yellow tops are interesting. Contrary to advise on t'internet, both of mine are manual oiler only. The one pictured is a low hour saw, with I think likely original hard nose bar. This one has an air leak on a seal, but its a very strong saw. The black top is a torque monster, and I reserve it for nasty jobs like railway sleepers as its got a .404 chipper chain.