I have a (by a previous owner) fully restored BN4 from -57. The cylinder head has been replaced with a later 6 port version (AEC 960) and it has two HD6 carburettors. The engine runs like a dream and it is proper quick. Are there any exterior differences between the 2.6 liter block and the 2.9 liter version. The engine number matches the chassis number and therefor it should be a 2.6 but the little plague is easily changed. It would be nice to know if my engine has been exchanged at some time. Thanks