can the engine mount of the 190E support the weight of the inline six. most of the time there is like 20 to 50 lbs. of tourqe that the rear end can take untill it collapes so u can get the rear end of the 300e too i belive its 3.06 or something.
the engine harness on both cars are different the distributor of the 190e only support 4 cylinders. the fuel pump relay is not the same. fuse box might not work. if you can just grab all you see in the bonet of the 300e, grab it just to make sure. just do a lot of research.

im also planning to do the same i got an 84' BMW 318i and the engine kind of gave up but it still starts. and i got a friend who got his rx7 3rd gen. rear ended totaled but the engine is not broken. so this might be the 1st rotary BMW in las vegas

and aslo i dont think the radiator on the 190e wont be able to cool down that 3.0 litter inline six