IIc has a super serial card on its motherboard, and by default starts up a 600,8,N,1 all I do is hit the firmware to change the baudrate to 9600, and again if I hook it directly to a PC, change the baudrate to 9600 I can talk to and from it all day at 9600,8,N,1
Can you try other characters and post what you get after the Arduino?
I have been typing in "hello world" and they all get the 7th bit as 1