In an email discussion with Rich Tworek the only way to learn the number would be to search the build cards at the Case plant in Racine and match it via the engine serial number assuming you have the original engine. Since I live in Houston this would be an expensive trip to find the number. Another method to get close would be to find someone with the same year model and compare engine numbers to get close. Not a bad route BUT Case didn't use number series groups for different size models. They were just applied to random tractors as they came down the production line.
Do you know the year model of your 630? I have stimated mine to be a 1960 model via the rear wheel casing date is 11-59 and the engine casting date is 1-60. Don't remember the exact day, I would have to go out to the shop and look but you get the idea.