Hello Charles, Yes you are right, it is a replacement taken from a TC model from around 1958-59. The "original" from my AD does indeed have the brass slotted core plugs. Not much else left though
I originally bought a job lot of three 102's. The SD without the original gearbox, a complete but rusty AD that had a completely shot water jacket, and the remains of a TC that had no magneto, tank, carb or prop. I have subsequently bought a nice complete AC that I will restore when I complete the SD and AD...
The AC I have has hexangonal core plugs!
The "original" AD and the replacement TC cylinders seem to have identical port configuration. Getting the cylinder off the AD was a job!
The AD has a bit of wear on both the small and big ends, so I'll be looking at that at some stage, before rebuilding. I have all the parts ready to go.