Excellent work! Nice video!
(I ordered five more MC33290
I have 2 MC33290 chips but, I have discovered that it is simply a voltage level converter. Therefore, I am using a LM393 DIP chip to convert my 12volt K-line to 5volt for my Arduino. Basically the LM393 is set-up as a dual comparator, one comparator is the TX from the Arduino with it's collector tied to 12v, and the other comparator is from the K-line of the bike with it's collector tied to 5v. I could e-mail a schematic to you if you need it. I have a few extra circuit boards for the LM393 level converter that I have made work for my Arduino.
I really like your project. My project is still early in development currently, I have a Bobuino board with RTC and SD card, a 2x16 LCD screen shield with buttons and my level converter circuit is a separate board. I hope to have a touch screen for a user interface then, have all other electronics hidden. In my case the Arduino will be in the back of my motorcycle and the screen will be mounted somewhere at the front of the bike.
I have one request if you don't mind, could you list your pin-out that goes with your code? When I say pin-out I mean: LCD pins- 9,8,7,6,5,4 etc. , SD card pins 10,11,12,13, button pins....... etc. It is OK if you want to keep some of your build secret, you have done a lot of good work.