Couple of observations. The amount of rust deserves a thorough descaling operation at the least. Check out your towbar mount bolts. I would hazard a guess the sleeve is simply cut off the original gooseneck - have never seen a hayman reece style hitch with a 40mm spigot. That towbar might need replacing get it checked by a towbar specialist would be my recommendation. My Hayman Reece has a 60mm outer to take a 50mm inner tongue.