it'll take years to lap a block w/ 600-grit paper. go to autozone and pick up an assorted pack of wet / dry sandpaper (the 9"x11" sheets) that has 220, 320, 400, and 600 grit papers. that'll work much better (and faster), trust me
also, what kind (formulation) and size (ID and wall thinkness) tygon tubing do you have? maybe some-1 will take it off your hands if you dont want it anymore...