Rubbolite lamps are earlier, then the WD pattern tail lamps were introduced, like your second pic...still wartime. Stamped on the bracket will be some letters, either L-WD-T (Lucas) or B-WD-T (Butler), one stop other tail as you say. I think it is likely that these lamps were in abundance after the war, hence why tractors might have been fitted with them. Due to the small lens area, they are not legal to use as road lights any more.
Your lamp, in second pic, does it have two contacts inside?, not for a stop/tail bulb though, this is possibly from a vehicle that had insulated return, usually armour, or petrol tanker perhaps. Butler front sidelamps also come with either single or double contact.