Its a big job, most probably will take many hours to get right and cost mucho dollars.
I make a few reproduction decals for vintage honda motorbikes. What I do is scan the originals, then take the image into my drawing app, hand draw all the lines and add fills, also have to correct where the screen print has shifted due to poor registration.
I can spend a couple of hours easy on getting a tank decal just right, can't imagine how long it would take to do a big job like yours, but then I work pretty slowly so maybe not so bad.
When I get a decal that is too large to fit in my scanner I do it in two sections. I place a piece of pin stripe masking tape in the middle of the decal so I can line the two images back up perfectly when finished. Its a bit cumbersome and I find myself tweaking one image as little as .10 degrees to get it lined up perfectly.
To scan a large area would be difficult but I guess not impossible, just depends on how determined you are.
Another thing that comes to mind is getting the colours just right, different printers can run different profiles and you may get a different shade from what you were expecting. Of course I am just a novice so someone with more experience might be able to do it a lot easier.
Anyway, just my two bobs worth.
