Adding a 20mm spacer would yield an offset of 15mm. The spacers will push the rim closer to the fender.35mm Offset plus the 20 mm would make it 45MM total offset. correct me if I am wrong (its been a while since I had my 420SEL) but they start with a lower offset stock wheel.
that might be close to being too much.
I might be wrong
What's the preferred terms for the "bolt to the hub then bolt the rim to the disk" vs the "use long bolts with the aluminum disk and do the rim and disk at the same time" thing??