A fuel injected M110 has 185hp. You'll need to find an earlier d-jet one to fit a W114 chassis and preferably out of a 107 or W114. They're quick.

If you want quicker, source an early M104 from an R129 which will have CIS. They make 230hp. I have a 300SL with that motor and a 5 speed dog leg manual gearbox and it's plenty quick, smooth and will rev to 7000rpm. I've been kicking the idea around of stuffing that drive train into a W114 myself. As it's CIS, there's less complication with wiring for the fuel injection.

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With best regards

Al