the cluster can be removed by pulling at the left side just there besides the left turn signal and at the rightturn signal level with the fingers pull equal or paralel . the oil pressure gauge needs a 10m.m. wrench.

for better space you can remove the stering wheel. prying out the horn pad you will find a allen 10mm. the stering wheel needs to pull to get out.
have a nice year. and congratulations the 300SD 1980-W116 is the most beatiful and luxory benz.
alberto mendez 300SD.