When I looked into installing a cylinder support system then they installed the brace first then machined the cylinders to account for any deformation caused by the brace. Is it the brace installation that's causing some of the deformation?
Here's "before" and "after" pics of my CSS installation --- the "before" block was scrapped. Note this CSS was installed and then block surfaced was "skimmed" to make it all one smooth surface. I also chose to use 77.5mm pistons, so a rebore was already in the plan.
Looks like your CSS is mounted below block surface, putting the top of the cylinder wall at risk --- questionable.
I highly recommend you do a rebore to 77.5mm. Altho, if your oval's largest diameter is still within cylinder specs, you might be able to get them all re-bored to 77.0Xmm (max spec diameter), then not have to buy another set of new pistons. Altho, if Arke is correct, an oversize rebore might be the only solution.
The copper ring is for an improved gasket seal and pistons are 9.0:1 CR.