I think you are limited somewhat on the rear of the 65-66 with tire width owing to that flat profile (skirt ready) of the opening. I have a 245/60/15 on the back of mine, on a 15x8 wheel, and there is not much room between the tire and WW lip.
Of course, wheels with custom offsets can give you more tire width. The fronts are a little more forgiving if the suspension is in good order (not sagged).
Members that are well versed in wheel and tire sizes will surely chime in.
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65 Laurentian post, 67 Grande Parisienne 4 door HT.