if you shim the bottom bush there is nothing to hold the shim stock in place as i said the bottom bush is free to rotate and has a gap already in it to allow for wear, like I said it's like a piston ring,
and if you need to 'peen' the top bush then you have other problems like the bush moving in the fork leg,which means the 'FORK LEG' is worn out, both these bushes are a transition fit which means a snug fit between fork tube and bush, if you start tightening up the bushing your accelerating wear in the bush or tube, i don't get it

Forks are simple