I'm 99% sure they are not interchangable. I have a 123 wagon and my neighbor has a 124 gasser wagon(should be the same third seat as on the diesel) and they are definitely different.

__________________
LRG
1987 300D Turbo 175K
2006 Toyota Prius, efficent but no soul
1985 300 TDT(130K miles of trouble free motoring)now sold