Dzeroplus
Method for preventing overspeed with both tachs and governor off, that I was taught anyway, was to very slowly back off the throttle until you get the low RPM horn and light and then just tweek the throttle back open slightly again to stop the warning.
Theory is RPM should be at 98-100%. This needs to be repeated every now and again to retain a reasonable rpm as the correlator can't cope by itself.
This was taught to me by a very experienced R22 instructor, who when I told him that the governor had failed, while I was on a check flight, sadistically said "even better, we can do practise autos with the governor off"...... B%^&$^d