Was your P4 replica designed to travel at such speeds and is it actually capable of exceeding 180mph?
The UK regulations say that the speed rating of the tyres needs to reflect the speeds that the vehicle was designed
to achieve, but there's a 'get out' clause for fast classics in that if W or Z rated tyres weren't available/fitted when the car was new you can still fit tyres to the same specification as the original equipment fitted at the factory (hope that makes sense?).
You'd have to check your local regulations (can't see there being too much bureaucracy in France...), but I would suggest that fitting the highest speed rated tyres that are actually available would be a sensible thing to do.
Love to hear more about your P4 and see some pictures, btw.