If your block and head are flat and just need a little clean-up, you can do that with sandpaper and a flat block of aluminum. Just be mindful of how much material you are removing and make sure you take about the same amount everywhere. I used 320-grit when I did mine and the Cometic MLS gasket I installed appears to be sealing just fine.
I did the same thing to my old ST165 about 10 years ago and it has held a seal ever since. (That engine has other problems now, but is thankfully in the hands of a new owner.)