My '88 V63 has thicker horns (and extra screws on the tailpiece) too. Funny that I noticed it just when I purchased my 4001CS and put the babies close together for a "family picture"...
(see also how different are the neck joints)
So I posted my question on the official Ric forum, and Mr. John Hall said that my V63 looked like a 4003S with vintage pickups option, but I purchased the bass brand new back in March 1989 (from an authorized dealer), and my warranty paper says "4001V63 FG".
Plus, the neck has the correct heel, the correct toaster position, the correct TRC and the whole hardware reflects the V63 standards...
My guess was that the wrong body wings got glued to a V63 neck, so I wrote an e-mail to Rickenbacker, enclosing several pictures. The answer was that "since the entire production is handmade, some little differences are possible".
Of course, I would have expected a more detailed explanation. I would never sell my bass, but if I did, how could I call it? I would have been satisfied with a simple declaration of my bass' particular "status" from Rickenbacker..... but I never got a real reply...