Hi
a few points:-
Don't fit 16" tyres on 400mm wheels. It isnt safe and there is a very big chance they will not be round. 400mm is a bout 15 3/4"
I beleive in period Lancia fitted Michelin X and Pirelli on their cars, but i think the Flaminia was Pirelli (Please correct me if i'm wrong.)
when you buy a Michelin or a Pirelli tyre you are assured of quality in both instances. However in this instance you are looking at different handling characteristics which i hope to explain.
the Michelin X is a great tyre and when it cam out, at the end of the 1940s it was a completely amazing tyre, as the first radial tyre offering more grip and dramatically increased longevity. They weren't sports car tyres, they did offer mor grip but it wasn't progressive. often some drivers found that they could still get better lap times becuase of the grip, but the consequences of lack of grip was sudden.
Pirelli developed the Cinturato in 1952 as the next radial, but a radial tyre that was built with sports cars in mind, so the extra grip and longevity, however with progressive handling, so when you were on the edge of grip you could still power round a corner progressively, and importantly predictably, which is important with sports cars of the period.
As a result sports cars of the period innitially would tentertively start using the Michelin X, then whole heartedly take on the Cinturato, as a result in period Lancia fitted Michelin X on its family car versions and then Cinturato on its Sports cars.
the 175HR400 Pirelli Cinturato is 12mm taller in diameter than the 165HR400 Cinturato and 8mm taller than the 165SR400 Michelin X.
Although the Michelin X 165SR400 is taller than the 165HR400 Cinturato, i would expect the rolling radius to be similar, or maybe even the Pirelli to be taller, becuase the Pirelli has a stiffer side wall, so less sag in the carcass.
Noet the sports car tyre the Pirelli Cinturato has an H speed rating.
Personally i hate white wall tyres on a European sports car, (which is tricky when my job is actually flogging these tyres) But Michelin do make a 165SR400 X with a white wall. we can also have a white wall built into the 175HR400 Cinturato if you need it, but Black wall is best.
It really is worth fitting the Pirelli. dont be fooed by budget tyres. (I hope these attachment s work. they are of 2 independent tyre tests, showing how dreadful budget tyres are.
I hope i have answereed all the questions on here. Basically just fit the Pirelli Cinturato, and yes the Coupe does fit 175HR400 Cinturato CA67, and Pirelli do make them speccially for your car.