If you have a burette and a dial indicator with a magnetic base, you can figure it out for certain. I'd venture a guess you'll be somewhere in the 8.2-8.5:1 range realistically.
I have the dial indicator and the magnetic base to place on the deck (two of them, in fact), but I don't have the burette. At least, I don't think I have one. Will have to check.
You sure compression would be that high given the open chambers combined with the dished pistons? That's better than I would have hoped for with this combination, quite honestly. Not that I don't want to improve it though - and dished pistons just make me fearful of pinging and over-rich carb settings to (poorly) compensate.