We had 2 units (170431/2) re-engined a few years back with more powerful MTU engines to resolve the underpowered problem. They went like stink but unfortunately were much noisier and quite unreliable with 2 minor fires occurring so the project didn't get any further
Am I right in thinking that the more powerful MTU Engines were both the same as the MTU units in the 172s - and didn't get on with the gearbox on one of the 170/4s, managing to break one? IIRC the unit that ran as a 2 car for a while as a result.