Oh yes, please. Another oil thread!
Short but unpopular because much too simple answer: the M30 is a relatively modern construction (hard to believe as it dates from 67-68 ).
Still:
Go synthetic (don´t worry, all that "too thin and it´ll leak and all that" is BS).
Use 0w40 or 10W60.
Don´t use 0w30, that´s for more modern motors.
Forget about "Classic Oil". Might as well call them Snake Oil. Most profitable product oil companies make: Cheapest imagnineable stuff in a pretty can.
Oil (especially modern synthetic) is so much better today than in the 60s and the oil filter in the M30 is pretty effective: Go for 10.000mls change intervalls on full synthetic. Even 15.000mls would do no harm.
Forget all additives. Good oil has plenty and finely matched to each other. Additional additives are like vitamin pills. Only americans believe in them. Do little harm but absolutely no good. Most gets pissed away.
Do not warm the engine by leaving it to idle. Start the engine, wait 3-4 seconds for full oil pressure and drive off.
Drive it gently (no full throttle and no more than 2500rpm) until the oil has warmed.
Install an oil temp gauge.
Once you get the oil to at least 70deg Celcius: go for it.
Stop worrying.
Drive it hard and have fun.