We have a 2.6 5 speed 190. It seems to me that all the suspension parts are interchangeable excluding bars and the diff. We have 124 springs and 201 arms+knuckles with 4 piston 124 brakes. Looking at some M103 and M104 blocks I've had around it looks like the engines would be bolt in swaps but the wiring would be difficult. We've thought about it.

How did you like your 129 springs? What would you do differently with your suspension setup? Our 400E stuff causes us to lift an inside rear which is not ideal.