you can look at the engine identification number, i'm pretty sure it is located above the starter motor, but i might be wrong
the motor is either an S50B30 or an S52B32
the S50B30 is the 3.0 liter engine found in 95 m3's and the S52B32 is the 3.2 liter engine found in the 96-99 m3's
there's an easier way you can look at the 10th digit of the vin number located on the driver's side door jamb
if the 10th digit is S, then it is a 1995 which would make it a 3.0l engine
if the digit is T,V,W, or X then it is 96+ model which would make it a 3.2l engine
also the 95 engine has obd1, and the 96+ has obd2
if your already sure it's a 96 then the engine is the 3.2l with obd2