Just a thought. Why don't you just buy a cheap GPS. You can pick a 3-1/2" one up for 30.00 to 40.00. I used one last summer, they are pretty much water resistant, but if you are worried you can buy a waterproof case on Ebay for about 20.00.
I'll bet it's a lot cheaper than buying the speedo kit from BRP plus its more accurate and you can measure distance tell direction, and won't have to worry about getting lost, and you won't need to update it since you won't need to worry about new roads.
I just used the suction cup and stuck in near the dash, I also made a teather out of a piece of string in case it cames loose you won't lose it.
Here's one for 40.00 which even has an MP3 player.
http://www.bensoutlet.com/products/nextar-x3-gps
Lou