I know GM can build a twin turbo V8. I've seen them do it. You could look back to my days and find several renditions of the firebird that had twin turbo V8's.
Way back when I was a field service tech I was fortunate enough to visit the GM tech center in Detroit. That was there main research and development facility and they produced many different prototypes. Unfortunately they would destroy anything they ever made after its purpose was fulfilled including whole cars. Well one of the bean counters there found that there was a lot of money being spent on transportation and utility vehicles so they had the idea to distribute prototype vehicle to the employees for use on sight and for utilitarian purposes instead of destroying them after use.
The maintenance person that I was with was given an S10 pickup truck with a 454 twin turbo engine. He took me out on the test track and I can say without a doubt that that was the scariest and fastest vehicle I have been in to date.
So I have no doubt that GM can do it well.
