The best way to find 6 degrees on a 1969 Olds 350 Rocket timing tab is with a diagram which can be found in a repair manual. The timing markings are on the pulley.
15 degrees before top dead center
Should- that is only a couple degrees & can compensate with distributor.
I didn't see a specific year year you're interested in, however a 1978 Olds 403 is listed as 18 degrees initial timing (detach and plug vacuum advance hose while setting initial advance).
Set by dwell 28-32 degrees approx. .017
The timing is supposed to be 8 degrees before top dead center (tdc). But, when you first start it up it (the ecu) will advance the timing to 12 degreees before (tdc) for quicker easier starting, I'm guessing. When it warms up it should be 8 degrees before (tdc).
my money says the 350 olds rocket seeins how there was never a 357 chevy.
More bottom end torque!
timing CHAIN
My book only goes back to 1974. In 74 the timing for both the 230hp & the 275hp was 10 degrees before top dead center @ 1100 rpm. you may find that it likes 12-14 degrees better.
The the 1969 OLDS 98 had 365HP
Chain.
18 year olds got the vote in the UK in 1969 with the passing of the Representation of the People Act 1969. It came into effect for the 1970 general election.