Yes, you need those shims. Some kind of shims, anyway. When I restored my LM, I did not get all of the shims back in. Somehow when it was reassembled - even with most shims in place - the lens assembly was far enough off to cause one side of the frame to be out of focus. I checked alignment and sure enough, it was off by a mm or so. I made some thin plastic shims and installed them on that side and it corrected it well enough that I couldn't see a problem with it any more.