When I had my 1978 plus 8 the only way it would pass the emissions was if I disconnected the pipe from the head to the carbs /inlet manifold. So there would be blue smoke coming out through the louvres but the exhaust had the sensor placed in it. The MOT chap used to say, "I'm not required to look or measure the bonnet area"
Fun days...
My kind of MOT tester....

Approaching 40 years old, my Mog might not require an MOT test next year, I need to check up on the date of first registration, though the regs might have changed by then...!