Wow! Interesting project!
Wish I could help, but I'm not the bits and bytes sort of guy.
One of the guys I work with designed and built a custom OBD2 interface/display for his Harley V-Rod.
He wrote his own assembly code, though.
More info at this forum:
http://www.v-rodforums.com/forums/showthread.php?t=17092
Also the manual is available (1MB):
http://www.v-rodforums.com/forums/attachment.php?attachmentid=28782

I thought you guys might like to see another OBD user interface.

Good luck on the work- I'm 'lurking' as you progress, always interested.
My car has OBD1 (95 Honda), but I'm not sure if OBD1&2 functionality is your goal. (I should probably read through all the previous OBD posts...)