The 3.1 was the ESSEX v6 which was a much better engine as far as tuning was concerned, the 2.8 is the cologne v6 which has Siamese exhaust ports on each head where as the Essex had 3 branch manifolds, I had the three port heads from the boss mustang from the states on my 2.8 Granada which bolt straight on to the cologne block with no modifications needed, coupled with a four barrelled Holley carb sat on top, my Granada was carb not injection.

With the 2.8i cologne I’d defo look into changing the exhaust and manifolds to a janspeed or something like that, change the cam shaft as well, but without doing a twin turbo conversion, boring the block out or slipping laughing gas into it you can’t screw much more power out of them, I had my 2.8 in my Granada bored out to 3.1, as above cam, exhaust and carb conversion and she made around 180 bhp iirc