Old farm equipment, a trailing hay rake from Blackstone & Co

Today me and my hubby had our annual Boxing Day walk in the countryside. Here in the South East is quite common to see some old farming equipment on the fields left to rust and rot. The letters are still readable, so we know this hay rake was made by Blackstone & Co, Stamford. Actually it is called Lister-Blackstone tractor rake (fourth pic). I can't see any date on it but I learned from the internet the company was taken over by R. A. Lister & Co in 1937, so this giant rake can't be older than that.