Hi, nice catch.
If I remember it correctly, ref. 1827 is slightly smaller than the 811 (i.e. Yacht Club), but otherwise they are pretty much the same.
I suppose it has a 854 movement.
Someone already suggested the moeb site in order to have a date. Keep in mind that there are two serial numbers: one for the case and one for the movement. Those numbers are quite close, but they are different. I suppose yours should be around 1.9xx.xxx.
Congratulations and welcome among the IWC from the early '70s enthousiasts.
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