Not a job I would ever want to tackle again. However, I was reasonably succesfull using the following method. Use some rubber lubricant on the outside of the rubber bush but not on the inside unless absolutely necessary. Push the rubber bush about 1/3 to 1/2 into the fork end then push the metal bush into the free end by hand until it won’t go further. Put the whole assembly into the vice and squeeze the metal bush into the fork end. With luck it will take the rubber in with it squeezing it thinner as it goes. You may have to try this several times before you get it right. The rubber bush elongates and thins down as its pushed into place.
Lubricating the outer part of the rubber bush helps it to slide into the fork end. Not lubricating the inner helps create enough friction to push the rubber bush into place rather than simply sliding the metal part straight through. At least that’s the theory. It worked for me in the end – but never again