From what I understand the oil cooler was an option on the earliest MGBs before becoming standard fitment. Then a funny thing happened with the 1974 1/2 (first big rubber bumper cars) MGBs. While the roadsters kept the oil cooler and front anti-roll bar (IIRC), the MGB GT lost those and I recall the BL rep for our zone stating that they added enough weight to the slightly heavier GTs that they could not get them emission certified if they were included. Even with those removed they could not get the GT certified for the 1975 model year so those 1974 1/2 GTs were the last ones officially available in the North American market.
Funniest thing (to me) that he ever showed or told us was related to the "MG - Still One Jump Ahead" ad campaign (1973?) where they parachuted an MGB on a skid out of the back of a C-130, along with a parachuting soon to be driver. In the ad, he lands by the car, unstraps it from the skid and drives away as other non-BL sports cars attempt to catch it. He had some still pictures from the the ad filming, including several from the first attempt at the ad. Guess what didn't open on the first filming attempt, yep, that's right. Included were a couple of still photos showing a Damask Red MGB, shiny side down and compressed to about 18" high.