Sorry about taking so long.
A 280 S Transmission will work just fine. It is geared a little different that a 280SE Coup but you really won't notice. a 280S has a 3.92 rear (euro spec). If you want to get a 3.25 you will need to find a U.S. spec 280SE 4.5. or if you want a 3.69 rear end you will need to find a 280SE 3.5 or 4.5 European spec.
the 3.25 will offer the best top end proforance, low rpm, high top speed.
the 3.69 will offer more bite at the low end with a little higher rpm at the high end.
either way, both are much better than a 3.92 or a 4.08. rear end.
All of these closed end rear axles will fit your coup with out any problems.
If you still would like the transmission #, it will take a few days I'm out of town.