DVLA are now asking for photos a lot more.
It's now common for them to ask for proof that a car exists ie, photo of the car and VIN location, when applying for a new style V5 replacing the old style blue V5.
Not having a photo of the original car displaying it's original registration number might be an issue and DVLA will probably ask for one.
I would recommend doing some research on your car and you might find a photo or reference to it.