At 1-1/4" I.D. diameter for the headtube, that's 1/16" clearance in radius, accommodating the thickness of the cups. Sounds like 1-1/8" diameter steerer to me.

You might also comfort yourself that in any case, 1-1/8" is the most common standard steerer by far for recent vintage bikes and is the most likely to fit.

Looking over the pics, you may wish to take the frame in to an expert to determine what type of headset is needed, whether integrated or "standard" and use a tool like the FSA gauge:



Or research the frame brand and find out what was original spec for the model.