According to the info i had read recently, the valve seats in 1000's & 1200's are aluminium bronze alloy for the inlets & cast iron for the exhausts. If this is true, then it would be wise to slip in a squirt of valve seat lube at tank top up time.

Unleaded fuel is specificly recomended against for use in L series engines in the fuel company literature that i have studied here in Australia. Lead replacement fuel was specificly recomended.
Unfortunately i can not bring to mind the source material for the Datsun 1000 & 1200 valve seat material at this moment.