E30 Zone

Have just swapped M40 318 for a M20 320 i have swapped over what i thought was a 320 tacho coding plug but still the revs are miles out the redline means the needle being 6oclock in the mpg gauge!
Could anyone advise me of the correct part number plug that is required for a 320. Its a 1989 model.

I presume there isnt anything else required to ensure rev counter works accurately?

Thanks Alex