You could slacken the bolts holding the shelf up and shim between the shelf and the wall. Also, rather than replace the feet you can put washers between the feet and the deck to level it. You don't need adjustable feet.
Most turntable do not have adjustable feet.
My own solution for levelling my Planar 10:
IMG_4216 by Chris Tarling, on Flickr
IMG_4217 by Chris Tarling, on Flickr
Why not simply adjust the entire rack? I assume it's on adjustable spikes/
P8 heavy and squashes one of the feet????