The replica is being constructed with two Suzuki Hayabusa engines coupled together. But if, IF it is successful in flying, someone might put up money for replica Bugatti engines. I expect someone has made patterns for new 50B engines by now - you can certainly get replica T35, T51 and T57 motors. That IF is highly relevant, because the plane had radical geometry, untried prop drive arrangements, and the control arrangements are complicated and uncertain. The control systems of the original were entirely in boxes, so it's a jig-saw puzzle to guess how it was supposed to be assembled and adjusted, assuming all the right bits are there - and no extraneous bits get mixed in.