I assume you mean a 1966 250SE... [If you had another car in mind, let me know]
Quoting the 1966 TDM...
- With the engine not running and the battery reading atleast 11v, the pressure down stream of the filter should be 0.8 to 1.1 kg/cm-squared (which is 14.88 lbs/square-inch).
- At the overflow valve of the injection pump, the pressure should be AT LEAST 1.3 kg/cm-squared.
- Fuel should be delivered at that same point at a rate of AT LEAST 3 liters/minute.
- The point gap should be 0.3-0.4mm, resulting in a dwell of 37-41 degrees. For new points aim for the 41 figure. Also test dwell at idle and 4000rpm. If there is a deviation of greater than 3 degrees, rebuild the distributor.
There is a great writeup of mechanical fuel injected systems http://www.pelicanparts.com/techarticles/911_MFI/TipMFI.htm