Hi Paul!
Those look pretty HC indeed. If I had to guess I would say somewhere around 11:1?
Like I have already stated elsewhere, I am running my A10 on forged Wisecos (9:1). It goes reasonably well and I haven't had any problems up 'til now, although it's an iron head model and its actually 9,3:1 (head and barrels skimmed). The A7 runs on 9:1 (with 8,75:1 JP pistons and skimmed alloy head).
If you want a reliable and sturdy engine I would not go any higher than somewhere around 9:1.
By increasing the compression ratio, you impose more stress on the bearings, the conrods, the conrod bolts and you have a higher combustion temperature = more thermal stress on the cyl. head material. And naturally starting gets a bit more difficult. And as you are using the 357 cam the effective compression will raise, too.
Maybe you could have those HC pistons machined off a bit on top if the material is thick enough? I would not reuse the other ones, they look like they have seized and probably the ring grooves aren't any good either? Have you checked them?