Unless an absolute shed load was spent, I think it would look just like a standard 4 door saloon with the rear doors welded up!
A coupe's doors are generally wider with the pillar pushed further back; I saw an edition of Custom My Ride a few weeks ago, where they took a large 4 door Merc and turned that into a coupe... It was a huge job!
The leading edges of the rear doors were cut off (about 5-6 inches) and welded to the rear edges of the front doors.
What was left of the rear doors were turned into the rear quarter panels.
Custom made glass and door cards had to be installed as well as major modifications to the interior.
As previously mentioned, I would rather just go for a GT!
"Looking through the knothole in Granny's wooden leg"