I also believe that some of the posts are making this a little too
complicated. It's unlikely minor differences in keel shape will be
noticeable cruising - I bet a new sail or two would have a much bigger
impact. The Carter 33 was a very fast boat in it's time.

I am not a naval architect and you do the following at your own risk.
I'm also assuming you don't care about resale value - since you got the
boat for almost nothing. What I would do is a low cost test. Cut 9"
off the keel for a 4' 8" draft (wear a respirator) and chock the cut
off piece in the bottom of the bilge. The whole boat only displaces
8000lb so the last 9" of this fin keel isn't going to be very heavy-
you could cut it into smaller pieces so you don't hurt your back or so
it fits better in the very shallow bilge space in this boat. Then see
how the boat sails - she will be more tender -- so start off with a
reef in the main and a small jib. Get a good feel for any stability
changes. If it's too tender, you'll need to find a way to put more lead
at the bottom of the keel - but you may feel it's fine for your
purposes. Forget this whole plan if you ever think will do real
offshore work and tell any future buyer what you did!

Another plan - and safer - is to call Bob Perry. He worked with Dick
Carter when your boat was designed (as did a lot of other now famous
designers). He should know the boat and might have some creative
thoughts. Or he'll tell you it's a big mistake. Either way it won't
cost you much and you'll learn a lot of things about your boat besides
the keel.

Here's a link:

http://www.perryboat.com/page/consult

And enjoy the Carter 33. It's a great boat.

Carl