If your just looking at the car, and its manual, the 215 will have the 6 speed, and the 185 will have the 5 speed.
The console will reflect this, 5 speeds have normal exec console (but the inner is black, not grey) and the 6 speeds have the calais/statesman style centre console.
I've also noticed that ALL 215s have the HSV 250k dash, and i've personally never seen a 185 with it, but theres other people on here who have seen them (either changed or thats how they are optioned). So if it has the 220k speedo, its def a 185.
Edit - oh lol, just realised you only meant the engine, forget about this