David was right in that you probably won't need to change any shims. If you do you can use a technique from the old Haynes that is not in the new Haynes. Basically you turn the camshaft so that the valve you are working on has the lob facing away from it then rotate the shim bucket until the notch faces towards you. With a big flat screwdriver you push the valve down by prying between the camshaft and the shim, insert a smallish flat screwdriver on edge between the camshaft and the shim bucket, relieve prying and as the bucket begins to rise, the small flatedge will hold it down. Now you are free to use a small pick in the notch to pop the shim out of it's bucket, you only need a few mils extra clearance. You will hopefully find that you can move shims around to do the clearances, if not volvo will sell you individual shims at no great cost, or you can pull some from your spare engine/scrapyard.
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patrick of montreal, '66/120, '83/245.