I've just been through this..
First thing I did was bought a dog bone, that helped but still knocking. What I'd recommend is taking off the drivers side engine mount, when you have the mount in your hand you'll see the rubber bumpers which control the forward and back movement. The rear rubber block will be worn away, the blocks should have a peak on them, mine was worn flatter than the front one. What I did was to take the metal part of the mount (effectively the cup that the rubber bumpers stop against) and press it in a large vice to close up the gap between the rubber blocks, effectively removing the slack from the worn rubber. You can also pull the engine forward when refitting as the mount has a sort of adjustable sliding two part design.
I also replaced the passenger side gearbox mount. This is under your battery. A cheap part available from most motor factors. Mine was actually quite soft. Again, when refitting you can pull the engine forward.
Mine is now knock free even booting in 1st. It was really bad before.