This really is a trick question, if you rebuild something to the exact dimensions, schematics and use techniques or parts that they would have used, is it a replica? My HSC has the original chassis, reproduction floor plates, original armor, reproduction external storage bins, rebuilt engine with NOS parts, new wiring and fuel system, and new reproduced radiator. Is this an original or reproduction? Halftracks and carriers with reproduction armor, wheels that get new rubber etc. If you start with something that is original and have to reproduce components I would consider it an original with some reproduced parts. Look at the jeeps out there, you can get complete jeeps that every single component could be reproduction. I think it really depends on how you look at it. So my Cromwell started life as a Cromwell, then modified into a Charioteer and will be turned back into a Cromwell, I will probably not be able to find a turret, so a reproduction turret will be made, but to exact specifications, thickness with original pieces and reproduction pieces, when the Cromwell is finished is it an original or reproduction? Reproduction to me is reproducing something to make it look like an original, such as the SdKfz 222s, Stug's, Pzr IIIs, kooble cars etc.