Think the best investment would be a fuel pressure tester which will let you verify the control and system pressure.
I went out and bought a tester from JC Witney for about $60 which may not be the best tester out there did let me set the control pressure on my Warm Up Regulator on my 84 380sl - it was running way lean beforehand - now has the needed power and now tackling the Idle Speed Controller -
If you do order the fuel tester make sure it is for the Bosch CIS system and it will come with the necessary fittings or adapters to work with the MB.