I have mounted Campagnolo alloy ultra-torque cranks on an otherwise classic bike to get a 50/34. They are Stiffer. You can notice it. You might have to upgrade your chain or fab very thin spacers between the rings. I went with a 9 speed chain and Ultra spaced freewheel. Look out of place? Perhaps. At least its alloy. I think carbon cranks would look odd. I have another vintage hot rod project, it will get dual pivot brakes and compact carbon cranks, painted to match the frame. I can always exchange parts back for the period correct concours judges of which there are hardly any anyway, especially on the West Coast. Meanwhile I will ride it more and have fun.