hi people,
i need a suggest to lapping this:

specifically, I need to remove that little difference, on the side where there are those three holes.. this:


the height of the 'step' I think it is less than 0.5 mm .. do you think I can proceed normally?
or, I was thinking to trying to put a strip of scotch transparent (which is very thin and with abrasive paper 400 should not ruin) on the rest of the base, and try to work a little only on the 'step', and then, after, continue lapping the entire base ..
also, because it is structurally very different from a tower cooler, I could lapping making him move on sandpaper only in this sense:

any suggest??
thnx!