Well, with a 400 litre v8 in a 124 coupe, whether a 300 or 320CE, , you will be a wolf in sheeps clothing. AFAIK all 124 coupes have a six cylinder engine...at least those badged 300CE or E320, which would be 88 thru 95, I think.

Look at it like a 500E.. normal 124 body, but a tiger under the hood.

Good luck with the conversion.