The important things for the compression are to be adequate and even. I don't have 420 information is front of me, but you would certainly want to see 125 +/- 10%.
If oil consumption is reasonable and oil pressure is good, the bottom end is probably OK.
The right side is clearly hosed with bent valves. The left side has a couple of low readings. You have to fix the right side to get the car to run. I would think you are looking at another 3-4 hours of labor plus a few hundred dollars at the machine shop to do the left side.
I would say that this (both sides) is the minimum investment if you are going to keep the car. If you decide to sell it just do the right side and have some XP33 run through the engine to see if you can improve the compression.
There used to be a saying "If you valve, you've got to ring." The theory was that good compression would put pressure on worn rings and cause additional oil consumption. But I haven't heard anyone say that about the later Mercedes V8's.
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe