An emotive topic... They who are without sin can only throw the first stone comes to mind!
It's the classic trade off between authenticity, and reality, Original Pattern, and Original Parts:
Original Renovated Vehicle (totally original parts)
Original Restored Vehicle (parts replaced, but restored it's original state)
Original Pattern Vehicle (original vehicle rebuilt to match a genuine vehicle)
Replica Vehicle (built to match exactly a genuine vehicle, bar some 'swap over' parts)
Look Alike Vehicle. (built from outset to only depict an original vehicle.
Take an example of a Willy's Jeep. You can change everything, with new parts, so if you do that, is the vehicle truly original? but then if the parts are 100% exact copies, then is that really harmful? The thing really lost is petina, and service damage. But a lot of restorations take most of this out anyway.
How many Jeeps would be with us now if we didn't have these shiny new parts? far fewer!, so extensive part replacement isn't a bad thing, as long as sellers are honest about originality.
Almost no spitfires would be flying now, unless substantial replacement was acceptable.
And when restoring a vehicle, sometimes you have to fit used parts of the same type, but in better condition, for example fitting an engine from another vehicle that is in a running state. For our Morris C4, we are fitting a running engine from a later (postwar) vehicle, as it saves about £4000 on the bill. The original engine will be kept, and restored at a later date, if the 'temp' unit is wears out.
If a vehicle is so rare it's totally gone, then a replica is fine, but to what extent do you copy the original? I think a very close copy is acceptable, but there must be a will to eventually create a 100% exact vehicle. If you don't have an original engine and drivetrain, then maybe ensure the vehicle is built in a way to eventually retrofit one.
Another example is our Morris. It was a Radio truck, but nearly nothing remains of the Back Body. Not even information, or patterns. The whole vehicle is so extensively deteriorated, there is a huge amount of work just building a rolling chassis, so we are building a GS version for now, but in a way where any future owner could simply swap parts for the correct items, or build to 100% original spec.
So the day our Morris is finished, it will look amazing, but only be 30% of the original vehicle by weight? but 100% authentic to an original WW2 vehicle, 70% to it's original build. It will be capable of being 100% one day, with about 50% of originally fitted parts.
Some things can be acceptably altered, like a design that was weak, or unsafe, but the alteration should still look as close as possible to an original.
I've seen some WW2 vehicles with 8.8 metric fasteners on them, and even steel sizes vary, and can be spotted.
But for our Morris, even though it deviates in some ways, it will still have original pattern steel, fixings, wiring, ect, ect.
I think building a Replica, and not bothering to even try and keep to original pattern design, and fit, is a lost opportunity. It is possible to make something as accurate as it can be, with an approach to allow later alteration.
Why is a Replica being built? is it simply as part of a bigger display, when it's inclusion, helps tell a story? (i.e. an important historical event, or to show an activity) For example a Fibreglass Spitfire on a genuine queen Mary Trailer, to show how they were recovered.
But building an entire WW2 tank hull with welded 12mm steel, instead of rivetted 50mm plate, is changing it's historical context from the original so far, it's no longer possible to 'back engineer' it.
If a Replica's design, from the outset, ignores the aim to upgrade it later to an authentic pattern vehicle, it is not even worthy of the term 'Replica', and the term 'Look alike' is more accurate.
Sometimes a Lookalike is totally fine, for instance for re-enactors, who don't want to spent £2million for a German Tank!
But if the Replication, is going to be the centre of any long term historical collection, then to spend fortunes, building it incorrectly, is a bit of a waste. Yes, we can't afford to build it 100% correct for now, but we can build what we can, with an aim to one day, someone else improving it to a more authentic replica.
The future for restoration is bright, and with modern tech, even the most impossible to recreate parts in 50 years, will be within reach of restorers, so why not think about the future, and build a Replica, than can easily be upgraded?