I think it would be fine. 9.8:1 is less than the GX engine's 10:1 compression ratio.

USA 91 octane "Premium" is probably equivalent to:
AUS 96 octane "Super"

Which is equivalent to:
pre-1973 - 96 octane
1973 - 92 octane

It depends on the rating method (MON, RON or (R+M)/2) used at the time and country.

Details: club article: Fuel Requirements

Lead Replacement Additive is not required for Datsun 1200 stock valves and valve seats. They are already engineered for lead-free fuel.


Btw, many of the new 2008 models have 11:1 compression ratio. The 2008 Corvette is 505 HP, yet gets 24 mpg. None of these cars need racing gas or any additives, just the "Premium" fuel available at every Gas Station.