Your flywheel will fit the 560 Motor. You will need to rework a bit the 450 intermediate plate to fit it on the 560 motor, it has been done, and it is certainly much less work than adapting 560 heads on a 450 motor. See here:

560SL Manual transmission conversion, Crank position sensor Help? - Mercedes-Benz Forum

You can do the same with the M119. the challenge will be the crank sensor. You may then fit a 560 timing cover which will allow you to fit a 450 or 500 ignition distributor so that you can get rid of the sensor and all other electronics. Not sure the M119 will fit the r107 engine bay though.