Well, a little bit at odds with the other posters, I think salvage shims are absolutely fine. You should be able to get what you need (I have had no trouble) and carry a reasonable micrometer or fine caliper. Used shims show no wear that I can detect. And I find that these engines do require shimming, especially with 100 K or more of neglect, or with a change of cams. You might get lucky and find you are within tolerances, but plan to shim if you are doing more than one engine in a lifetime. You will see most shims you find are in a narrow medium thickness range and getting the occasional thick or thin shim to expand your collection is where all the fun is. The biggest issue is breaking the varnish glue that tends to hold the shims in the cup. I use a fine pick to nudge them enough to break the hold. Good practice is had in the salvage yard. Good luck.