Quote: Thats one hell of a statement. 1 bar of boost [all day, every day], stock pistons, no 'O' rings, as it isn't going to be serious. [15psi in an A series not serious ]

First thing, ... homework.

What kind of pistons do other engines that run 1 bar of boost use? What kind of rings do they use as well?
What about their head gasket design, is it significantly different around the fire ring than an A series gasket?

At the very least, I think that hypereutectic pistons would be needed [12% silicon content or more] if such things exist, while stock Datsun pistons are very likely to be of the money saving hypoeutectic type [less than 12% silicon content]
Hypoeutectic are just fine in low stress stock Datsun engines, but aren't real happy as the boost [& heat] start to rise.

Ignition timing seems to be critical & you need to be able to retard the spark more & more as the boost rises, & water injection is one of those things that helps to keep detonation under control. Think about it.

Personally, I would build the engine & run it at about 7psi for a while. Run it in at this lower figure.

Once you have it sorted, push it to about 10 psi & make sure there is no detonation. After that, it's up to you, but that would probably see the conservative little-old-me out. I like engines that live long [& prosper]