I once read in a book about nightfighters that the British could have removed the guns from their heavies, which weren't much good at night anyway, and their speed would have picked up to close to 300mph. This would be a tough ask for WW2 nightfighters to intercept. I think Tony may even do this in his book?
They did take out the mid-upper turrets from Lancs and Halifax's and then left the nose turret off Halifax's making it better aerodynamically as well.