As you found, because the minimum gap is only 0.03mm, it is difficult to measure the clearance if it is near the lower limit and calculate the shim size needed, but if you can rotate the tappet freely with your finger, you know you have a positive clearance between 0 and the size of your thinnest gauge, so if you subtract 0.05mm from the current shim size, that should put it in the acceptable range (-0.10 would leave too big a gap). If it is too tight even to do this, another option is to remove the shim and stack your feeler gauges to measure the total gap between the cam and the tappet where the shim sits (I don't bother to add up all the different sizes, it's more accurate to measure the total thickness of the stack with your micrometer). For safe cleaning of gasket material from aluminium surfaces, I use a scraper made from a scrap piece of aluminium. Because it's softer than the surface, it needs to be sharpened frequently on a flat sheet of abrasive paper, but there is no risk of damaging the joint face, and it cleans the old gasket off effectively.
As you found, because the minimum gap is only 0.03mm, it is difficult to measure the clearance if it is near the lower limit and calculate the shim size needed, but if you can rotate the tappet freely with your finger, you know you have a positive clearance between 0 and the size of your thinnest gauge, so if you subtract 0.05mm from the current shim size, that should put it in the acceptable range (-0.10 would leave too big a gap). If it is too tight even to do this, another option is to remove the shim and stack your feeler gauges to measure the total gap between the cam and the tappet where the shim sits (I don't bother to add up all the different sizes, it's more accurate to measure the total thickness of the stack with your micrometer).
For safe cleaning of gasket material from aluminium surfaces, I use a scraper made from a scrap piece of aluminium. Because it's softer than the surface, it needs to be sharpened frequently on a flat sheet of abrasive paper, but there is no risk of damaging the joint face, and it cleans the old gasket off effectively.
😎👍😎