JimF:

Your manual values don't seem to be consistent; that is they don't have a monotonic relationship of resistance to retard value!!

From the 1986 190E 2.3-16V Introduction to Service Manual:

No resistor = no retard
2.4Kohm resistor = 2 degree retard
1.3Kohm resistor = 4 degree retard
750 ohm resistor = 6 degree retard (standard in my US car)
470 ohm resistor = 8 degree retard
220 ohm resistor = 10 degree retard
0 ohm resistor = 12 degree retard

European cars had a 7 position switch with these resistor values installed to allow compensation for poor octane gas.

I would listen for "pinging" under load after you remove the resistor. Hopefully your car is easier to check the timing with a timing light.

Good luck.

Tom