I think ever since 2009 or so, SSC has used an engine of their own design(but the block is still based on a GM LS-series racing motor). I think this new one is just the old engine in DOHC form, bored out to 6.8L. Don't know if the turbos are different/bigger, but they shouldn't be; the Ultimate Aero was running relatively low boost for how much power it was putting out. 14psi,when most cars making 1000+hp are running 20psi or more. Veyron: 19/SS: 22(rounded up)
Venom GT: 20
Agera R: 20
So I guess it would be fair to say that SSC's engine, as it is now, is as much a Chevy as Koenigsegg's is a Ford. As in, not at all.