There is a company that sells on e-bay that makes 90 degreee adapters and can calibarate the difference in tire size and all that good stuff to get your speedo right. I had a similar problem with a shifter change from the column to th floor. I got one of those and it solved the problem. Check out this link. Hope this helps.

Mike

http://cgi.ebay.com/ebaymotors/Speedometer-Gear-Cable-90-Degree-w-25-Ratio-Adapter