Old cab, reportedly well-proportioned (6)
I believe the answer is:
hansom
'old cab' is the definition.
'reportedly well-proportioned' is the wordplay.
'reportedly' indicates a 'sounds like' (homophone) clue.
'well-proportioned' becomes 'handsome' (I've seen this before).
'handsome' is a homophone of 'HANSOM'.
(Other definitions for hansom that I've seen before include "Type of cab" , "Two-wheeled horse-drawn covered cab" , "transport from the old days" , "Two-wheeled one-horse carriage" , "Two-wheeled horse-drawn covered carriage" .)