Using the Russian EPC on
EverythingBenz - Mercedes-Benz Forum and Web Search Using Google I've come up with this for you.
(This is how I started to compile the data presented in the thread I've linked above)
I've had to make some assumptions.
I'm assuming the 190E is a 201.024 chassis
Mercedes Benz EPC 201.024 Chassis Information | Everything Benz
and I'm assuming the 300E is a 124.030 chassis
Mercedes Benz EPC 124.030 Chassis Information | Everything Benz
From the links above you can see that the W201.024 had the 722.400 transmission and the W124.030 had either the 722.320 or the 722.358 transmission
Digging deeper you can find that the differential on the W201.024 has a 1:3.23 final drive and the W124.030 had a 1:2.87 final drive - so from that I can say that the shift points will be a bit messed up.
Back to the question - specifically will it fit
The engine fitted to the W124 is a M103.983 / M108.980 starter on the LHS of the vehicle
The engine fitted to the W201 is a M102.961 / M102.962 starter on the LHS of the vehicle
So it looks good.
This is as far as I can take you as I don't have grown up EPC ('cos it costs money for non US residents!)
I can't compare or check adapter plates for you (I assume they exist).