IMHO, you should maintain the W123 or if u want to change the engine, u can always opt for another Merc engine like 260E, 300E, and by doing so, nothing much to be done as it share the same mounting as the W124, except for the wiring system. W123 is going to be a classic car soon, thus by changing to Japanese rocket engine you have totally changed the spec of the car, IMHO, driving a continental car with Japanese engine is just like driving a Super Japanese rocket in a Mercedes shell. Why should scrap your chassis partially merely to get the Japanese engine fit into your car? Plus, although u maintain its original look such as the interior, the driving passion has changed, it is not a Merc anymore. I am not sacrificing all the comfort, stability, durability of my car merely for power. IMHO if u want performance car, get one and dont sacrifice the continental car to fill ur insatiable lust for power. Here are some differentiation between RB20, 1JZ, 2JZ and the M102 and M103 engine. The Mercedes Benz M102 and M103 engine uses timing chain meaning that this engine is maintenance free, just look after the lubricant oil, coolant and etc. RB20, 1JZ, 2JZ, 1G, 5M engine are powerful, undeniable but it requires regular maintenance such as the timing belt (it is shameful when those W123 drivers knew that u changed the timing belt where else they have been using the original engine without problems as they are using timing chain), turbo maintenance (was informed that it is very costly). Mercedes Benz are a true work horse. Just think about it, sorry if I have offended any of you here, but this is what I have been keeping to myself all this while, I am sad of seeing this magnificient W123, it is supposed to get another Mercedes engine. The half cut for W124 260E and 300E are getting cheaper nowadays though. Just some thought.
