I'd guess it won't cause low compression or oil usage, that depends mostly on how you set your ring gaps and how you CC the head/piston dish. Might cause a tiny loss of power or increased wear over the next 100,000 miles. More piston slap? Datsun tolerances are already higher than Detroit of the same era, so it probably won't hurt

Maybe you can swap pistons around until they are all in spec

So the machine shop measured everything and still got it out-of-spec -- which happens all too often. That's why I prefer to do it myself