What engine do i need for a 1994 BMW 318i?

Hi, I recently bought a new engine for my 1994 BMW 318i, which was from a 1992 318i. The problem came when it arrived and the mechanic told me it wouldn't fit. I now have to buy another engine but don't want to make the same mistake again. Could anyone out there please, please tell me how not to throw more cash away and the differences between the engines (mine has the coolant pipes at the rear of the head and a plastic oil filter housing)?
Thanks very much, all the best. Rich