5 arm 135bcd? All you can do without buying a new crankset , is make the outer chain ring smaller .

Campagnolo Carbon fiber cranksets, I see, online just now, are now are 4 arm and offer 50-34t combinations..

Super Record crankset - Components Campagnolo..





Hope Your 'braze on FD ' can move down to a 50t radius , though I expect a 53 -36 combo can be done ,

buy the 4 arm 53-39 complete, + a 36t inner ring and swap.

your bike got a 'power torque' 2 piece, external bearing BB already?