theyre not twins, 6.4 chargers are compounds, just like you would build for a 6.0.
Why do you ask is it going to be more money than its worth to make them work? Its the fact that the high pressure turbo is a vgt, this is the big problem, trying to get it to work right. You would need extensive tuning to get it right, if its even possible to do so with 6.0 programming. Youre also not going to get them to fit between a 6.0 intake manifold either, so youre going to need to swap intake manifolds, need custom up pipes, custom charge/intercooler piping, relocate the ficm etc.
Youre better off building a custom compound setup. If youre planning to do a high horsepower build, why on earth would you think making 6.4 compounds work would suffice? In all honesty in the long run, its going to be cheaper and less of a headache to build a compound setup.