Those are the low compression pistons, like what was said the smaller cambered magnums would bump the compression up from where it is now. I'm betting around 8.8 to 1. Makes for a doggy motor if you ask me.

The last 340 I built and have driven now a lot was the KB243 pistons which stick out .029 above the deck and I went with edlebrock open chamber heads which gives me 10.1 to 1. The motor makes way more power than with stock heads and stock 2 valve relief hi compression pistons.

I run a 600 which performs great for me.

The timing chain slop looks about normal to me?