Hi chaps

Pretty sure i've found this on here before but i'm trying to find out exactly what engine i have fitted to my 21. its either a 28 or 21 motor.

is there a way of distinguishing which going off the engine number or are there other ways of identifiying it?

Also intrested in how to distingiush the differances visually or by number of the 21 and 28 flywheels.

ANy help appreciated.

Cheers