1. This trick MIGHT have worked on a 450SL, but I haven't gotten it to work on a 380SL or a 560SL. You gotta remove the harmonic balancer, which is a PITA,but not really all that difficult.
2. You gotta remove the distributor
AFAIK. Again, not terribly bad.
I strongly recommend that you have at the very least the shop manual on CD for this. The block is aluminum and stripping a threaded hole in an aluminum block is Very Bad. Use a torque wrench after looking up the values.
Keep in mind that this is a six hour by-the-book job. Be glad you are doing it.