Personally, I find it hard to distinguish between the XK120 and 140. What're the tell tell signs of differences? A checklist essentially? Bumpers etc.

 

Read all about it here: -

https://en.wikipedia.org/wiki/Jaguar_XK140

 

Lovely stuff, cheers Fraser. Tell tale: larger bumpers with overriders

 

The bigger bumpers were put on because so many US car drivers parking technique was to manoevre into the space by listening for a bang at either end then changing direction ! The flimsy XK120 bumpers couldn't withstand this. There were other, hidden changes that improved the car too. Actually the XK140 production figures are less than either of the XK120 or XK150 cars. Largest production was the XK120.

 

The engine in a 140 is further forward giving more leg room but making The car a little more tail happy. The 140 has rack and pinion steering to the 120’s recirculating ball making the steering feel more precise.
The engine power was increased as the car aged going from 160 in the earliest 120 to 210 in the 140 MC