Two wastegate ?
You could one run off of a single bank. I've also done that in the past, but depending on your power level, some swear that it will make the engine wear unevenly between banks.
Someone here ran a setup with the hotside almost identical to the one you pictured, and ran a single wastegate that had a small tube coming off of each bank and merging right next to the turbo. With a 60mm gate he was able to control boost really well.





