It was no a reinforced bumper, but to note a reinforcement of the mounting point. there should be an EMEI about it on the series 3 EMEI page.
Veh G 307-19, Issue 1 - Truck Utility LightWeight MC2 Land Rover Series 3
Reinforcing of front bumper mounting. 5 pages A4. Feb 87
which I just realised is not online. I will try and put it up today once I finish catalouging the auction vehicles.