Most of the new ones are 27x40 while the originals are 27x41 or at least mine is. But it might be only on the ones used at theaters.
I have numbers on mine too.
830156 then Christine under it at the lower corner next to Columbia Pictures logo.
National Screen Service Corporation with other writing.
Your lucky, mine is folded and I still haven't got a frame for it since Walmart doesn't have my posters size. My friend Bill who owns one of the screen cars has his in a back lighted frame that gives the glow of Christine a sweet effect.