All right Eddie, Arcade mode is using another files than regular Rally mode. So you should copy some files from favourite car bunch, rename them and paste onto game Cars folder. Now be careful... copy *a1.bfl and *a1N.c3d files twice, rename copies as *c3.bfl , *d3.bfl and as *c3.c3d , *d3.c3d
For better understanding see the example snapshot - the same thing do with other cars
Attachment 3050