Fuel is unleaded.
The kind of usage these classics get over here, the unleaded issue really doesn't come up.
Every one in our local club has been running their classics (including my self) for decades now on unleaded without using hardened seats and no one has had any issue.
Since I will be removing the same weight of material from each piston, will it affect the balancing of the rotating components ?
I can imagine that if some Pistons were lighter than the other it would affect the balancing