People have been rebuilding Mustangs for a lot of years. I believe that Mr. Becks P-51 was a ground up build.
As for the Flugwerk's parts being great, yeah, it is nice for another source to become available. The big problem though is that they are all "experimental" use only, so any type certified birds (most in the US are either limited or standard) are SOL. Plus, add to it the continued effort of the FAA to curtail Experimental Aviation, and the risk will be that the parts will be unusable in the US.