Chris,
I seem to remember a drawing and an explaination of the foil shape on a Hobie rudder in "Welcome to A Fleet" "Book 1 Boatspeed".
Trying to change the "shape" on those old Lexan (plastic) rudders is a time consuming and thankless task. I've never had any success doing anything more than smoothing them a bit and putting a finer point on the trailing edge. Maybe I'm a bit impatient when working with that material as the inherent flaws with the medium (too much flex under pressure when sailing) are hard for me to get past mentally.
I liken working with Lexan rudders to mud wrestling with a pig, it wastes your time and you get all muddy. ( altho i doubt if the Lexan enjoy's it)
If you figure your time is worth something, it doesn't take long until buying a new set starts to look pretty good.
I bought a used boat once just to get the Old EPO's. Took off the EPO's for myself, put back on a set of Lexan's and resold the boat for the same $$ that I bought it for.
Good luck in your quest.
Stephen