I used the Fuel Injection Pump Timing/Locking Pin the last time I did mine. That is the method that takes the least skill to do.
You 1985 Engine if it has the original Fuel Injection Pump will have the port for the Timing/Locking Pin.
Fuel Injection Pump Removal with the Oil Filter still on 617.952
Fuel Injection Pump Removal with the Oil Filter still on 617.952 - PeachParts Mercedes ShopForum
I cannot comment on the bubble method as I have never tried it.
I have done the Drip Method. A little time consuming as I had not done that since the 1970s but it worked (I was trained at work to do the Drip/Flow Timing Method so at one time I had a lot of practice at it).
2 things they help you no matter what timing method you use.
One is to scribe a mark acrossed the Fuel injection Pump Flange and acrossed the Engine Block so you can get the Pump back to the same spot if you have trouble.
Two remember you are only going to need to move the Fuel Injection pump a tiny amount (your timing is only going to be a degree or 2 late) and that is easiest to do if you disconnect all of the Fuel Injection Hard Lines.