First you must determine if the vehicle is behaving normally for a diesel, or whether it's truly slow on launch. This is best done by driving another W123 for comparison.

Then, if it is slow, the most important things to check, in sequence, are the following:

1) Valve clearances
2) Cam timing (chain stretch)
3) Injection timing


Once all of those are set properly, then you may consider additional fuel by adjustment of the ALDA. But, without verification of the three points, above, I would not make any ALDA adjustment.