The 17 was first introduced at the end of 1985, so there's no way it's a '70s boat
That's interesting. I'm refinishing the hulls on an H17 that sounds almost identical to this boat in terms of the shape it is in, and the model number I have is CCML1614F78. That is hand written into what must be the original gelcoat because there is nothing but fiberglass under it. Doesn't that mean it was made in June of '78?
To answer the questions in the original post, one of my centerboards is in bad shape, and I've found some used ones for sale on ebay, $65 - $135, though they do say that they show a few cracks. I think they are interchangeable. I don't see any obvious differences between the two I have, and when I've priced new ones online, I don't see them listed separately, just a single part number for a centerboard.
As far as sailing without the centerboard for testing purposes, I'm sure it will work. You won't win any races, but I'm sure it will sail.