I have 165/65/13 tyers but on Alpine wheels, there was little problem with the clearance in the back, I used good old method and pulled the wings with my hands.
The tyre guides suggest a maximum of 145 tyres on 4 inch rims, though Angel said that 155 tyres aren't a problem. I suspect 175 tyres would be too wide for the rims.
They'd fit Gordini rims (are they 5.5 inch?) and there shouldn't be any clearance problems (other people run them). Though the gearing would be a little too high.
I have seen two R4s with 165 tyres on GTL wheels, don't remember the profile, but I remember one of them had the rear tyre tread very close to the outer suspension arm mountings, so it must had been higher profile than 65.
Oop - forgot about the rear suspension. 145/85 tyres get close to that with their slightly bigger diameter.
My thought on tyre diameter is the diameter of say a 155/70 tyre would be roughly the same as a 165/60. It's a rough calculation but works for one or 2 changes in section.
Might be worth measuring the distance between the standard 135/85 tyre and the rear suspension outer mounting, then using one of the tyre calculators on the internet to work out if you'd get away with the 175/65. Still think the 175s are too wide for the standard rims though.
oh well
shame as ive got 3 almost new ones sitting here,and the car im thinking of having needs 4 tyres
anyone have a good set to sell? maybe a couple of wheels too as 2 are really rusty
cheers
matt