there should'nt have been that much to mod really, as they are essentially the same, and if you had bit from a 156 (plastic top) and a 155 block and head (alloy top) its just a case of sensors and pulleys.
For the ecu (computer) you will have a code light on if the original code box is still fitted with any ecu other than your original, to cure this you will need a ecu, code box, and the chips from the keys from a car equippet with a 2.0l 16v twinspark with the plastic top (155bhp)
The reason is because your key contains a chip, the chip signals the code box to unlock the ecu and allow it to start and run, thus meaning with out the key the car wont start, unfortunatly the key chip is unique to the code box which in turn is unique to the ecu so all must used together and cannot EASILY be cross swapped with other items. HTH
Right, but the problem was that the guy who runs this whole swap operation:) has already tried to mount a 156 2.0TS ECU, code box, and swapped the key chips. Still, the car didn't start...