Lots of hard work. Why not put an M104 3.2 in there? Standard W124 engine, all bits are available over the counter or via a breaker
The M104 has more power and will be a much smoother, 6-pot engine. If you want to make it a little different fit the M104 with an aftermarket ECU and dump the factory loom & ECU
I suspect E320 brakes will be fine for whatever you want to do
Nick Froome
the independent Mercedes Estate specialists