Maximum Allowable Variance in Deck Height, Stock 2.0 Liter Four Options

[motorvated]

I'm in the process of re-assembling the top end of my stock 2.0 liter four, and I have measured deck heights as follows:
#1 - 0.036
#2 - 0.029
#3 - 0.037
#4 - 0.035

These measurements are with the cylinder base sealing rings in place and the cylinders torqued down snugly and measured with a dial gauge. To me it seems as if I need to add a shim to the bottom of cylinder #2 approx. 0.050 - 0.080 to increase its deck height to within the range of the others. I have a couple of used 0.080 shims, one of which I could add to cylinder #2 to bring it up to 0.037.

I have a couple of questions about this.

First, how much variance is permissible between the measurements? If the deck heights are all within 0.002 of one another, is that Ok or do they need to be exactly the same.

Second, can I re-use one of my 0.080 shims or should I source a new one.

And third, do I place the shim on top of the cylinder sealing ring, beneath it, or doesn't it matter. I was planning on putting it on top of the sealing ring.

Thanks in advance for your advice.