For what it's worth, I did poly on one of my previous Mk1s and found it transferred too much of the engine vibrations to the rest of the car.

I didn't like it

(but thankfully that one wasn't a daily driver so didn't matter too much).

I do remember some people in the past drilled through their poly bushes here to soften them up a bit but I never tried that.

Not that I have the part numbers

(sorry!) but are you after the mount itself

(metal) or the insert?