Actually the service literature from M/B states that the 116, 117 cylinder heads should not be surfaced for warpage as they are soft enough to conform to the block when torqued. At high enough mileage to be apart most do need surfacing for corrosion, though.

With the engine apart for the head job, you should disassemble the intake manifold and replace the rubber rings that seal the upper to lower sections. With your mileage they are leaking vacuum-guaranteed.